From 30e9a3f6b366c473a58b199a074abc845a80d330 Mon Sep 17 00:00:00 2001
From: Scott Olesen <ulp7@cdc.gov>
Date: Wed, 15 Apr 2026 19:09:17 -0400
Subject: [PATCH 01/10] Put contacts into network file

---
 examples/network-hhmodel/main.rs    |  2 +-
 examples/network-hhmodel/network.rs | 57 +++++++++++++++++++
 examples/network-hhmodel/seir.rs    | 85 +++++++++--------------------
 3 files changed, 85 insertions(+), 59 deletions(-)

diff --git a/examples/network-hhmodel/main.rs b/examples/network-hhmodel/main.rs
index fee887dc..e6d14b76 100644
--- a/examples/network-hhmodel/main.rs
+++ b/examples/network-hhmodel/main.rs
@@ -43,6 +43,6 @@ fn initialize(context: &mut Context) {
     let to_infect: Vec<PersonId> = vec![context.sample_entity(MainRng, Person).unwrap()];
 
     #[allow(clippy::vec_init_then_push)]
-    seir::init(context, &to_infect);
+    seir::init(context, &to_infect, 1.0);
     context.execute();
 }
diff --git a/examples/network-hhmodel/network.rs b/examples/network-hhmodel/network.rs
index e9bd7061..d5ae36de 100644
--- a/examples/network-hhmodel/network.rs
+++ b/examples/network-hhmodel/network.rs
@@ -1,15 +1,19 @@
 use ixa::network::edge::EdgeType;
 use ixa::prelude::*;
 use ixa::{HashSet, HashSetExt};
+use rand_distr::Bernoulli;
 use serde::Deserialize;
 
 use crate::loader::{open_csv, HouseholdId, Id};
+use crate::parameters::Parameters;
 use crate::{Person, PersonId};
 
 define_edge_type!(struct Household, Person);
 define_edge_type!(struct AgeUnder5, Person);
 define_edge_type!(struct Age5to17, Person);
 
+define_rng!(NetworkRng);
+
 #[derive(Deserialize, Debug)]
 struct EdgeRecord {
     v1: u16,
@@ -58,6 +62,59 @@ fn load_edge_list<ET: EdgeType<Person>>(context: &mut Context, file_name: &str,
     }
 }
 
+fn sar_to_beta(sar: f64, infectious_period: f64) -> f64 {
+    1.0 - (1.0 - sar).powf(1.0 / infectious_period)
+}
+
+/// Get all the contacts a person will have over a certain duration
+pub fn get_contacts(context: &Context, person_id: PersonId, duration: f64) -> HashSet<PersonId> {
+    let parameters = context
+        .get_global_property_value(Parameters)
+        .unwrap()
+        .clone();
+
+    // Probability of contact during the duration. Note that this assumes that the duration is not too high!
+    let p_hh = duration * sar_to_beta(parameters.sar, parameters.incubation_period);
+    let p_other = duration
+        * sar_to_beta(
+            parameters.sar / parameters.between_hh_transmission_reduction,
+            parameters.incubation_period,
+        );
+
+    let mut infectees = HashSet::new();
+    infectees.extend(
+        get_contacts_by_edge_type::<Household>(context, person_id)
+            .iter()
+            .filter(|_| context.sample_distr(NetworkRng, Bernoulli::new(p_hh).unwrap())),
+    );
+
+    infectees.extend(
+        get_contacts_by_edge_type::<AgeUnder5>(context, person_id)
+            .iter()
+            .filter(|_| context.sample_distr(NetworkRng, Bernoulli::new(p_other).unwrap())),
+    );
+
+    infectees.extend(
+        get_contacts_by_edge_type::<Age5to17>(context, person_id)
+            .iter()
+            .filter(|_| context.sample_distr(NetworkRng, Bernoulli::new(p_other).unwrap())),
+    );
+
+    infectees
+}
+
+/// Get the contacts by edge type
+fn get_contacts_by_edge_type<ET: EdgeType<Person> + 'static>(
+    context: &Context,
+    person_id: PersonId,
+) -> HashSet<PersonId> {
+    context
+        .get_edges::<Person, ET>(person_id)
+        .iter()
+        .map(|e| e.neighbor)
+        .collect()
+}
+
 pub fn init(context: &mut Context, people: &[PersonId]) {
     // Create dense household networks
     create_household_networks(context, people);
diff --git a/examples/network-hhmodel/seir.rs b/examples/network-hhmodel/seir.rs
index 80aa7b80..574b2bb6 100644
--- a/examples/network-hhmodel/seir.rs
+++ b/examples/network-hhmodel/seir.rs
@@ -1,11 +1,12 @@
+use std::collections::HashSet;
+
 use ixa::log::info;
-use ixa::network::edge::EdgeType;
 use ixa::prelude::*;
 use ixa::{impl_property, ExecutionPhase};
-use rand_distr::{Bernoulli, Gamma};
+use rand_distr::Gamma;
 use serde::{Deserialize, Serialize};
 
-use crate::network::{Age5to17, AgeUnder5, Household};
+use crate::network::get_contacts;
 use crate::parameters::Parameters;
 use crate::{Person, PersonId};
 
@@ -27,38 +28,18 @@ define_property!(
     default_const = InfectedBy(None)
 );
 
-fn sar_to_beta(sar: f64, infectious_period: f64) -> f64 {
-    1.0 - (1.0 - sar).powf(1.0 / infectious_period)
-}
-
 fn calculate_waiting_time(context: &Context, shape: f64, mean_period: f64) -> f64 {
     let d = Gamma::new(shape, mean_period / shape).unwrap();
     context.sample_distr(SeirRng, d)
 }
 
-fn expose_network<ET: EdgeType<Person>>(context: &mut Context, beta: f64) {
-    let infectious_people = context
-        .query(with!(Person, DiseaseStatus::I))
-        .to_owned_vec();
-
-    for infectious in infectious_people {
-        let edges = context.get_matching_edges::<Person, ET>(infectious, |context, edge| {
-            context.match_entity(edge.neighbor, with!(Person, DiseaseStatus::S))
-        });
-
-        for e in edges {
-            if context.sample_distr(SeirRng, Bernoulli::new(beta).unwrap()) {
-                context.set_property(e.neighbor, DiseaseStatus::E);
-                info!(
-                    "Person {} exposed person {} at time {}.",
-                    infectious,
-                    e.neighbor,
-                    context.get_current_time()
-                );
-                context.set_property(e.neighbor, InfectedBy(Some(infectious)));
-            }
-        }
-    }
+fn expose(context: &mut Context, infector: PersonId, infectee: PersonId) {
+    info!(
+        "{infector:?} exposed {infectee:?} at time {}.",
+        context.get_current_time()
+    );
+    context.set_property(infectee, DiseaseStatus::E);
+    context.set_property(infectee, with!(InfectedBy, Some(infector)));
 }
 
 fn schedule_waiting_event(
@@ -106,34 +87,22 @@ fn schedule_recovery(context: &mut Context, person_id: PersonId) {
     );
 }
 
-pub fn init(context: &mut Context, initial_infections: &Vec<PersonId>) {
+pub fn init(context: &mut Context, initial_infections: &Vec<PersonId>, period: f64) {
     context.add_periodic_plan_with_phase(
-        1.0,
-        |context| {
-            let parameters = context
-                .get_global_property_value(Parameters)
-                .unwrap()
-                .clone();
-
-            // infect the networks
-            expose_network::<Household>(
-                context,
-                sar_to_beta(parameters.sar, parameters.incubation_period),
-            );
-            expose_network::<AgeUnder5>(
-                context,
-                sar_to_beta(
-                    parameters.sar / parameters.between_hh_transmission_reduction,
-                    parameters.incubation_period,
-                ),
-            );
-            expose_network::<Age5to17>(
-                context,
-                sar_to_beta(
-                    parameters.sar / parameters.between_hh_transmission_reduction,
-                    parameters.incubation_period,
-                ),
-            );
+        period,
+        move |context| {
+            // get all infector-infectee pairs
+            let mut pairs = HashSet::new();
+            for infector in context.query(with!(Person, DiseaseStatus::I)) {
+                for infectee in get_contacts(context, infector, period) {
+                    pairs.insert((infector, infectee));
+                }
+            }
+
+            // do the exposures
+            for (infector, infectee) in pairs {
+                expose(context, infector, infectee)
+            }
         },
         ExecutionPhase::Normal,
     );
@@ -193,7 +162,7 @@ mod tests {
             to_infect.extend(people);
         });
 
-        init(&mut context, &to_infect);
+        init(&mut context, &to_infect, 1.0);
 
         context.execute();
 

From b17e223af0341632f8a49609806bb5b69957309b Mon Sep 17 00:00:00 2001
From: Scott Olesen <ulp7@cdc.gov>
Date: Thu, 16 Apr 2026 14:21:02 -0400
Subject: [PATCH 02/10] Bug and formatting

---
 examples/network-hhmodel/incidence_report.rs |  2 +-
 examples/network-hhmodel/seir.rs             | 27 +++++++++++---------
 2 files changed, 16 insertions(+), 13 deletions(-)

diff --git a/examples/network-hhmodel/incidence_report.rs b/examples/network-hhmodel/incidence_report.rs
index 874d9232..f0a806d7 100644
--- a/examples/network-hhmodel/incidence_report.rs
+++ b/examples/network-hhmodel/incidence_report.rs
@@ -158,7 +158,7 @@ mod test {
             let to_infect: Vec<PersonId> = vec![context.sample_entity(MainRng, Person).unwrap()];
 
             #[allow(clippy::vec_init_then_push)]
-            seir::init(&mut context, &to_infect);
+            seir::init(&mut context, &to_infect, 1.0);
 
             context.execute();
         }
diff --git a/examples/network-hhmodel/seir.rs b/examples/network-hhmodel/seir.rs
index 574b2bb6..38307ec3 100644
--- a/examples/network-hhmodel/seir.rs
+++ b/examples/network-hhmodel/seir.rs
@@ -2,7 +2,7 @@ use std::collections::HashSet;
 
 use ixa::log::info;
 use ixa::prelude::*;
-use ixa::{impl_property, ExecutionPhase};
+use ixa::{impl_property, ExecutionPhase, HashSet, HashSetExt};
 use rand_distr::Gamma;
 use serde::{Deserialize, Serialize};
 
@@ -34,12 +34,15 @@ fn calculate_waiting_time(context: &Context, shape: f64, mean_period: f64) -> f6
 }
 
 fn expose(context: &mut Context, infector: PersonId, infectee: PersonId) {
-    info!(
-        "{infector:?} exposed {infectee:?} at time {}.",
-        context.get_current_time()
-    );
-    context.set_property(infectee, DiseaseStatus::E);
-    context.set_property(infectee, with!(InfectedBy, Some(infector)));
+    let infectee_status: DiseaseStatus = context.get_property(infectee);
+    if infectee_status == DiseaseStatus::S {
+        info!(
+            "{infector:?} exposed {infectee:?} at time {}.",
+            context.get_current_time()
+        );
+        context.set_property(infectee, DiseaseStatus::E);
+        context.set_property(infectee, InfectedBy(Some(infector)));
+    }
 }
 
 fn schedule_waiting_event(
@@ -49,15 +52,15 @@ fn schedule_waiting_event(
     mean_period: f64,
     new_status: DiseaseStatus,
 ) {
-    let ct = context.get_current_time();
-    let waiting_time = calculate_waiting_time(context, shape, mean_period);
+    let t = context.get_current_time() + calculate_waiting_time(context, shape, mean_period);
 
-    context.add_plan(ct + waiting_time, move |context| {
+    context.add_plan(t, move |context| {
+        trace!("{person_id:?} changed to disease state {new_status:?} at t={t:?}");
         context.set_property(person_id, new_status);
     });
 }
 
-fn schedule_infection(context: &mut Context, person_id: PersonId) {
+fn schedule_infectiousness(context: &mut Context, person_id: PersonId) {
     let parameters = context
         .get_global_property_value(Parameters)
         .unwrap()
@@ -109,7 +112,7 @@ pub fn init(context: &mut Context, initial_infections: &Vec<PersonId>, period: f
 
     context.subscribe_to_event(
         move |context, event: PropertyChangeEvent<Person, DiseaseStatus>| match event.current {
-            DiseaseStatus::E => schedule_infection(context, event.entity_id),
+            DiseaseStatus::E => schedule_infectiousness(context, event.entity_id),
             DiseaseStatus::I => schedule_recovery(context, event.entity_id),
             _ => (),
         },

From 34691525fb501ec2ebcb1d4bb02de609d7d7b22a Mon Sep 17 00:00:00 2001
From: Scott Olesen <ulp7@cdc.gov>
Date: Tue, 28 Apr 2026 12:55:53 -0400
Subject: [PATCH 03/10] Rework example

- Repair tests
- Avoid mutable loops
---
 examples/network-hhmodel/README.md           |  32 ++--
 examples/network-hhmodel/incidence_report.rs |   4 +-
 examples/network-hhmodel/loader.rs           | 109 +++++------
 examples/network-hhmodel/main.rs             |  11 +-
 examples/network-hhmodel/network.rs          | 192 ++++++++-----------
 examples/network-hhmodel/seir.rs             |  16 +-
 6 files changed, 160 insertions(+), 204 deletions(-)

diff --git a/examples/network-hhmodel/README.md b/examples/network-hhmodel/README.md
index d338d09e..d920f51a 100644
--- a/examples/network-hhmodel/README.md
+++ b/examples/network-hhmodel/README.md
@@ -1,29 +1,27 @@
 # Example: Agent-based SEIR model with contact networks
 
-This example demonstrates the use of the `network` module of `ixa`.
+This example demonstrates a network model in `ixa`.
 
-There are three CSV files:
+There are three data files:
 
 - `Households.csv` represents 500 households of size 1-12. Individuals have age
   category and sex properties. Within the model, these individuals are placed in
   a densely connected network.
-- `AgeUnder5Edges.csv` contains the edges connecting those aged under 5
+- `AgeUnder5Edges.csv` contains the edges connecting those aged under 5.
 - `Age5to17Edges.csv` contains the edges connecting those aged 5-17.
 
-In `network.rs`, three corresponding edge types are created using the
-`define_edge_type!` macro and the networks are formed by adding edges to the
-context using `add_edge_bidi`.
-
-In `seir.rs`, a SEIR model is implemented with different betas by network edge
-type. Edge queries (`get_matching_edges`) allow us to identify the neighbors of
-the infected individuals and consider whether they become exposed.
-
-`loader.rs` reads in the `Household.csv` file and `parameters.rs` sets up global
-properties for the SEIR model.
-
-`incidence_report.rs` sets up a report with information on who became infected
-by whom during the simulation and saves the information to a csv in an `\output`
-folder.
+The simulation runs via:
+
+- `parameters.rs` sets up global properties for the model.
+- `loader.rs` reads in the `Household.csv` file and instantiates the people in it.
+- `network.rs` forms a dense network of household contacts, then reads in the other
+  contact files and instantiates those network edges. The edges are tracked as
+  model entities. This module also selects which individuals have effective contact
+  during each time period.
+- `seir.rs` manages transmission, infections, and disease trajectories.
+- `incidence_report.rs` sets up a report with information on who became infected
+  by whom during the simulation and saves the information to a csv in an `\output`
+  folder.
 
 ## How to run the model
 
diff --git a/examples/network-hhmodel/incidence_report.rs b/examples/network-hhmodel/incidence_report.rs
index f0a806d7..7ce23c56 100644
--- a/examples/network-hhmodel/incidence_report.rs
+++ b/examples/network-hhmodel/incidence_report.rs
@@ -145,8 +145,8 @@ mod test {
                 .set_global_property_value(Parameters, parameters.clone())
                 .unwrap();
 
-            let people = loader::init(&mut context);
-            network::init(&mut context, &people);
+            loader::init(&mut context);
+            network::init(&mut context, 1.0);
             incidence_report::init(&mut context).unwrap();
 
             context.subscribe_to_event(
diff --git a/examples/network-hhmodel/loader.rs b/examples/network-hhmodel/loader.rs
index 378d5fc3..ef3009c4 100644
--- a/examples/network-hhmodel/loader.rs
+++ b/examples/network-hhmodel/loader.rs
@@ -5,7 +5,7 @@ use ixa::impl_property;
 use ixa::prelude::*;
 use serde::{Deserialize, Serialize};
 
-use crate::{example_dir, Person, PersonId};
+use crate::{example_dir, Person};
 
 #[derive(Serialize, Deserialize, Copy, Clone, PartialEq, Eq, Debug, Hash)]
 pub struct Id(pub u16);
@@ -39,45 +39,26 @@ struct PeopleRecord {
     household_id: HouseholdId,
 }
 
-fn create_person_from_record(context: &mut Context, record: &PeopleRecord) -> PersonId {
-    context
-        .add_entity(with!(
-            Person,
-            record.id,
-            record.age_group,
-            record.sex,
-            record.household_id
-        ))
-        .unwrap()
-}
-
 pub fn open_csv(file_name: &str) -> Reader<File> {
     let current_dir = example_dir();
     let file_path = current_dir.join(file_name);
     csv::Reader::from_path(file_path).unwrap()
 }
 
-pub fn init(context: &mut Context) -> Vec<PersonId> {
+pub fn init(context: &mut Context) {
     // Load csv and deserialize records
     let mut reader = open_csv("Households.csv");
-    let mut people = Vec::new();
 
     for result in reader.deserialize() {
         let record: PeopleRecord = result.expect("Failed to parse record");
-        people.push(create_person_from_record(context, &record));
+        context
+            .add_entity((record.id, record.age_group, record.sex, record.household_id))
+            .unwrap();
     }
-
-    context.index_property::<Person, Id>();
-    context.index_property::<Person, HouseholdId>();
-
-    people
 }
 
 #[cfg(test)]
 mod tests {
-    use ixa::context::Context;
-    use ixa::random::ContextRandomExt;
-
     use super::*;
 
     const EXPECTED_ROWS: usize = 1606;
@@ -85,52 +66,52 @@ mod tests {
     #[test]
     fn test_init_expected_rows() {
         let mut context = Context::new();
-        context.init_random(42);
         init(&mut context);
         assert_eq!(context.get_entity_count::<Person>(), EXPECTED_ROWS);
     }
 
+    // Check there is exactly one matching entity
+    fn assert_exists1(
+        context: &Context,
+        id: Id,
+        age_group: AgeGroup,
+        sex: Sex,
+        hh_id: HouseholdId,
+    ) {
+        assert_eq!(
+            context.query_entity_count(with!(Person, id, age_group, sex, hh_id)),
+            1
+        );
+    }
+
     #[test]
     fn test_some_people_load_correctly() {
         let mut context = Context::new();
-        context.init_random(42);
-
-        let people = init(&mut context);
-
-        let person = people[0];
-        assert!(context.match_entity(
-            person,
-            with!(
-                Person,
-                Id(676),
-                AgeGroup::Age18to64,
-                Sex::Female,
-                HouseholdId(1)
-            )
-        ));
-
-        let person = people[246];
-        assert!(context.match_entity(
-            person,
-            with!(
-                Person,
-                Id(213),
-                AgeGroup::AgeUnder5,
-                Sex::Female,
-                HouseholdId(162)
-            )
-        ));
-
-        let person = people[1591];
-        assert!(context.match_entity(
-            person,
-            with!(
-                Person,
-                Id(1591),
-                AgeGroup::Age65Plus,
-                Sex::Male,
-                HouseholdId(496)
-            )
-        ));
+        init(&mut context);
+
+        // e.g., the person with data id 676 should be 18-64, female, in household 1
+        assert_exists1(
+            &context,
+            Id(676),
+            AgeGroup::Age18to64,
+            Sex::Female,
+            HouseholdId(1),
+        );
+
+        assert_exists1(
+            &context,
+            Id(213),
+            AgeGroup::AgeUnder5,
+            Sex::Female,
+            HouseholdId(162),
+        );
+
+        assert_exists1(
+            &context,
+            Id(1591),
+            AgeGroup::Age65Plus,
+            Sex::Male,
+            HouseholdId(496),
+        );
     }
 }
diff --git a/examples/network-hhmodel/main.rs b/examples/network-hhmodel/main.rs
index e6d14b76..a4eff47b 100644
--- a/examples/network-hhmodel/main.rs
+++ b/examples/network-hhmodel/main.rs
@@ -7,6 +7,8 @@ mod parameters;
 mod seir;
 use std::path::PathBuf;
 
+use parameters::Parameters;
+
 define_entity!(Person);
 define_rng!(MainRng);
 
@@ -27,14 +29,19 @@ fn initialize(context: &mut Context) {
     context.init_random(1);
 
     // Load people from csv and set up some base properties
-    let people = loader::init(context);
+    loader::init(context);
 
     // Load parameters from json
     let file_path = example_dir().join("config.json");
     context.load_global_properties(&file_path).unwrap();
 
+    let parameters = context
+        .get_global_property_value(Parameters)
+        .unwrap()
+        .clone();
+
     // Load network
-    network::init(context, &people);
+    network::init(context, parameters.between_hh_transmission_reduction);
 
     // Initialize incidence report
     incidence_report::init(context).unwrap();
diff --git a/examples/network-hhmodel/network.rs b/examples/network-hhmodel/network.rs
index d5ae36de..65b2f493 100644
--- a/examples/network-hhmodel/network.rs
+++ b/examples/network-hhmodel/network.rs
@@ -1,64 +1,67 @@
-use ixa::network::edge::EdgeType;
 use ixa::prelude::*;
 use ixa::{HashSet, HashSetExt};
 use rand_distr::Bernoulli;
-use serde::Deserialize;
 
 use crate::loader::{open_csv, HouseholdId, Id};
 use crate::parameters::Parameters;
 use crate::{Person, PersonId};
 
-define_edge_type!(struct Household, Person);
-define_edge_type!(struct AgeUnder5, Person);
-define_edge_type!(struct Age5to17, Person);
+define_entity!(Edge);
+// relative transmission rate
+define_property!(struct RR(f64), Edge);
+define_property!(struct Node1(PersonId), Edge);
+define_property!(struct Node2(PersonId), Edge);
 
 define_rng!(NetworkRng);
 
-#[derive(Deserialize, Debug)]
-struct EdgeRecord {
-    v1: u16,
-    v2: u16,
+fn add_bidi_edge(context: &mut Context, p1: PersonId, p2: PersonId, rr: RR) {
+    context
+        .add_entity(with!(Edge, Node1(p1), Node2(p2), rr))
+        .unwrap();
+    context
+        .add_entity(with!(Edge, Node2(p1), Node1(p2), rr))
+        .unwrap();
 }
 
-fn create_household_networks(context: &mut Context, people: &[PersonId]) {
+fn create_household_networks(context: &mut Context, rr: RR) {
     let mut households = HashSet::new();
+    let people: Vec<PersonId> = context.query(with!(Person)).into_iter().collect();
+
+    // for every person, check what household they are in
     for person_id in people {
-        let household_id: HouseholdId = context.get_property(*person_id);
+        let household_id: HouseholdId = context.get_property(person_id);
+        // if we haven't seen this household before, find all its member,
+        // and connect them in a dense network
         if households.insert(household_id) {
-            let mut members: Vec<PersonId> = Vec::new();
-            context.with_query_results(with!(Person, household_id), &mut |results| {
-                members = results.to_owned_vec()
-            });
-            // create a dense network
-            while let Some(person) = members.pop() {
-                for other_person in &members {
-                    context
-                        .add_edge_bidi(person, *other_person, 1.0, Household)
-                        .unwrap();
+            let members: Vec<PersonId> = context
+                .query(with!(Person, household_id))
+                .into_iter()
+                .collect();
+
+            for i in 0..(members.len() - 1) {
+                for j in (i + 1)..(members.len()) {
+                    add_bidi_edge(context, members[i], members[j], rr);
                 }
             }
         }
     }
 }
 
-fn load_edge_list<ET: EdgeType<Person>>(context: &mut Context, file_name: &str, inner: ET) {
+// Assert there is only one person with data ID `id`, then get their entity ID
+fn get_entity_id_by_data_id(context: &mut Context, id: u16) -> PersonId {
+    let v: Vec<PersonId> = context.query(with!(Person, Id(id))).into_iter().collect();
+    assert_eq!(v.len(), 1);
+    v[0]
+}
+
+fn load_edge_list(context: &mut Context, file_name: &str, rr: RR) {
     let mut reader = open_csv(file_name);
 
     for result in reader.deserialize() {
-        let record: EdgeRecord = result.expect("Failed to parse edge");
-        let mut p1_vec = Vec::new();
-        context.with_query_results(with!(Person, Id(record.v1)), &mut |people| {
-            p1_vec = people.to_owned_vec()
-        });
-        assert_eq!(p1_vec.len(), 1);
-        let p1 = p1_vec[0];
-        let mut p2_vec = Vec::new();
-        context.with_query_results(with!(Person, Id(record.v2)), &mut |people| {
-            p2_vec = people.to_owned_vec()
-        });
-        assert_eq!(p2_vec.len(), 1);
-        let p2 = p2_vec[0];
-        context.add_edge_bidi(p1, p2, 1.0, inner.clone()).unwrap();
+        let record: (u16, u16) = result.expect("Failed to parse edge");
+        let p1 = get_entity_id_by_data_id(context, record.0);
+        let p2 = get_entity_id_by_data_id(context, record.1);
+        add_bidi_edge(context, p1, p2, rr);
     }
 }
 
@@ -66,103 +69,72 @@ fn sar_to_beta(sar: f64, infectious_period: f64) -> f64 {
     1.0 - (1.0 - sar).powf(1.0 / infectious_period)
 }
 
-/// Get all the contacts a person will have over a certain duration
+/// Get all the effective contacts a person will have over a certain duration
 pub fn get_contacts(context: &Context, person_id: PersonId, duration: f64) -> HashSet<PersonId> {
     let parameters = context
         .get_global_property_value(Parameters)
         .unwrap()
         .clone();
 
-    // Probability of contact during the duration. Note that this assumes that the duration is not too high!
-    let p_hh = duration * sar_to_beta(parameters.sar, parameters.incubation_period);
-    let p_other = duration
-        * sar_to_beta(
-            parameters.sar / parameters.between_hh_transmission_reduction,
-            parameters.incubation_period,
-        );
-
-    let mut infectees = HashSet::new();
-    infectees.extend(
-        get_contacts_by_edge_type::<Household>(context, person_id)
-            .iter()
-            .filter(|_| context.sample_distr(NetworkRng, Bernoulli::new(p_hh).unwrap())),
-    );
-
-    infectees.extend(
-        get_contacts_by_edge_type::<AgeUnder5>(context, person_id)
-            .iter()
-            .filter(|_| context.sample_distr(NetworkRng, Bernoulli::new(p_other).unwrap())),
-    );
-
-    infectees.extend(
-        get_contacts_by_edge_type::<Age5to17>(context, person_id)
-            .iter()
-            .filter(|_| context.sample_distr(NetworkRng, Bernoulli::new(p_other).unwrap())),
-    );
-
-    infectees
-}
+    // Base probability of contact during the duration. Note that this assumes that the duration is not too high!
+    let base_p = duration * sar_to_beta(parameters.sar, parameters.incubation_period);
+
+    // Find all the people this person has edges to. Those people are contacts in this
+    // duration, with a certain probability
+    let mut contacts = HashSet::new();
+    for edge in context.query(with!(Edge, Node1(person_id))) {
+        let RR(rr) = context.get_property(edge);
+        let Node2(person2) = context.get_property(edge);
+        if context.sample_distr(NetworkRng, Bernoulli::new(base_p * rr).unwrap()) {
+            contacts.insert(person2);
+        }
+    }
 
-/// Get the contacts by edge type
-fn get_contacts_by_edge_type<ET: EdgeType<Person> + 'static>(
-    context: &Context,
-    person_id: PersonId,
-) -> HashSet<PersonId> {
-    context
-        .get_edges::<Person, ET>(person_id)
-        .iter()
-        .map(|e| e.neighbor)
-        .collect()
+    contacts
 }
 
-pub fn init(context: &mut Context, people: &[PersonId]) {
-    // Create dense household networks
-    create_household_networks(context, people);
+pub fn init(context: &mut Context, between_hh_transmission_reduction: f64) {
+    // relative risk of transmission between (vs. within) households
+    let rr = 1.0 / between_hh_transmission_reduction;
 
-    // Add U5 edges from csv
-    load_edge_list(context, "AgeUnder5Edges.csv", AgeUnder5);
-
-    // Add U18 edges from csv
-    load_edge_list(context, "Age5to17Edges.csv", Age5to17);
+    // Create dense household networks
+    create_household_networks(context, RR(1.0));
+    // Add other edges from csv's with lower transmission rate
+    load_edge_list(context, "AgeUnder5Edges.csv", RR(rr));
+    load_edge_list(context, "Age5to17Edges.csv", RR(rr));
 }
 
 #[cfg(test)]
 mod tests {
-
     use super::*;
     use crate::{loader, network};
 
-    const N_SIZE_12: usize = 1;
-    const N_SIZE_11: usize = 1;
-    const N_SIZE_3: usize = 122;
-
-    #[test]
-    fn test_expected_12_member_household() {
+    // Assert that person with `id` has `n` contacts (i.e., edges going from
+    // them, and also edges going to them)
+    fn assert_has_n_contacts(id: u16, n: usize) {
         let mut context = Context::new();
-        context.init_random(42);
-        let people = loader::init(&mut context);
-        network::init(&mut context, &people);
-        let deg11 = context.find_entities_by_degree::<Person, Household>(11);
-        assert_eq!(deg11.len(), 12 * N_SIZE_12);
+        loader::init(&mut context);
+        network::init(&mut context, 1.0);
+
+        let eid = get_entity_id_by_data_id(&mut context, id);
+
+        let n_to = context.query_entity_count(with!(Edge, Node1(eid)));
+        let n_from = context.query_entity_count(with!(Edge, Node2(eid)));
+        assert_eq!(n_to, n);
+        assert_eq!(n_from, n);
     }
 
     #[test]
-    fn test_expected_11_member_household() {
-        let mut context = Context::new();
-        context.init_random(42);
-        let people = loader::init(&mut context);
-        network::init(&mut context, &people);
-        let deg10 = context.find_entities_by_degree::<Person, Household>(10);
-        assert_eq!(deg10.len(), 11 * N_SIZE_11);
+    fn test_person_826() {
+        // Person 826 is in a household of 5 with no other contacts.
+        // There should be 4 edges going from them, and 4 going to them.
+        assert_has_n_contacts(826, 4);
     }
 
     #[test]
-    fn test_expected_3_member_household() {
-        let mut context = Context::new();
-        context.init_random(42);
-        let people = loader::init(&mut context);
-        network::init(&mut context, &people);
-        let deg10 = context.find_entities_by_degree::<Person, Household>(2);
-        assert_eq!(deg10.len(), 3 * N_SIZE_3);
+    fn test_person_243() {
+        // Person 243 is in a household of size 6 (i.e., 5 hh contacts)
+        // and has 4 other contacts
+        assert_has_n_contacts(243, 5 + 4);
     }
 }
diff --git a/examples/network-hhmodel/seir.rs b/examples/network-hhmodel/seir.rs
index 38307ec3..735aba3b 100644
--- a/examples/network-hhmodel/seir.rs
+++ b/examples/network-hhmodel/seir.rs
@@ -137,10 +137,8 @@ mod tests {
     #[test]
     fn test_disease_status() {
         let mut context = Context::new();
-
         context.init_random(42);
-
-        let people = loader::init(&mut context);
+        loader::init(&mut context);
 
         // set sar and between_hh_transmission_reduction to 1.0 so that
         // beta is 1.0
@@ -150,7 +148,7 @@ mod tests {
             sar: 1.0,
             shape: 15.0,
             infection_duration: 5.0,
-            between_hh_transmission_reduction: 1.0,
+            between_hh_transmission_rr: 1.0,
             data_dir: "examples/network-hhmodel/tests".to_owned(),
             output_dir: "examples/network-hhmodel/tests".to_owned(),
         };
@@ -158,7 +156,7 @@ mod tests {
             .set_global_property_value(Parameters, parameters)
             .unwrap();
 
-        network::init(&mut context, &people);
+        network::init(&mut context, 1.0);
 
         let mut to_infect = Vec::<PersonId>::new();
         context.with_query_results(with!(Person, Id(71)), &mut |people| {
@@ -170,19 +168,19 @@ mod tests {
         context.execute();
 
         assert_eq!(
-            context.query_entity_count::<Person, _>(with!(Person, DiseaseStatus::S)),
+            context.query_entity_count(with!(Person, DiseaseStatus::S)),
             399
         );
         assert_eq!(
-            context.query_entity_count::<Person, _>(with!(Person, DiseaseStatus::E)),
+            context.query_entity_count(with!(Person, DiseaseStatus::E)),
             0
         );
         assert_eq!(
-            context.query_entity_count::<Person, _>(with!(Person, DiseaseStatus::I)),
+            context.query_entity_count(with!(Person, DiseaseStatus::I)),
             0
         );
         assert_eq!(
-            context.query_entity_count::<Person, _>(with!(Person, DiseaseStatus::R)),
+            context.query_entity_count(with!(Person, DiseaseStatus::R)),
             1207
         );
     }

From 10b0245edbadc8a3639bdeaf87685437a61c9c1b Mon Sep 17 00:00:00 2001
From: Scott Olesen <ulp7@cdc.gov>
Date: Wed, 29 Apr 2026 09:25:12 -0400
Subject: [PATCH 04/10] fixup

---
 examples/network-hhmodel/incidence_report.rs | 2 +-
 examples/network-hhmodel/loader.rs           | 8 +++++++-
 examples/network-hhmodel/main.rs             | 2 +-
 examples/network-hhmodel/parameters.rs       | 2 +-
 examples/network-hhmodel/seir.rs             | 8 ++------
 5 files changed, 12 insertions(+), 10 deletions(-)

diff --git a/examples/network-hhmodel/incidence_report.rs b/examples/network-hhmodel/incidence_report.rs
index 7ce23c56..de8f6f99 100644
--- a/examples/network-hhmodel/incidence_report.rs
+++ b/examples/network-hhmodel/incidence_report.rs
@@ -124,7 +124,7 @@ mod test {
             sar: 1.0,
             shape: 15.0,
             infection_duration: 5.0,
-            between_hh_transmission_reduction: 1.0,
+            between_hh_transmission_rr: 1.0,
             data_dir: output_dir.to_str().unwrap().to_string(),
             output_dir: output_dir.to_str().unwrap().to_string(),
         };
diff --git a/examples/network-hhmodel/loader.rs b/examples/network-hhmodel/loader.rs
index ef3009c4..f9fd31d1 100644
--- a/examples/network-hhmodel/loader.rs
+++ b/examples/network-hhmodel/loader.rs
@@ -52,7 +52,13 @@ pub fn init(context: &mut Context) {
     for result in reader.deserialize() {
         let record: PeopleRecord = result.expect("Failed to parse record");
         context
-            .add_entity((record.id, record.age_group, record.sex, record.household_id))
+            .add_entity(with!(
+                Person,
+                record.id,
+                record.age_group,
+                record.sex,
+                record.household_id
+            ))
             .unwrap();
     }
 }
diff --git a/examples/network-hhmodel/main.rs b/examples/network-hhmodel/main.rs
index a4eff47b..f4c0abfb 100644
--- a/examples/network-hhmodel/main.rs
+++ b/examples/network-hhmodel/main.rs
@@ -41,7 +41,7 @@ fn initialize(context: &mut Context) {
         .clone();
 
     // Load network
-    network::init(context, parameters.between_hh_transmission_reduction);
+    network::init(context, parameters.between_hh_transmission_rr);
 
     // Initialize incidence report
     incidence_report::init(context).unwrap();
diff --git a/examples/network-hhmodel/parameters.rs b/examples/network-hhmodel/parameters.rs
index a32c4bce..f5ff0b52 100644
--- a/examples/network-hhmodel/parameters.rs
+++ b/examples/network-hhmodel/parameters.rs
@@ -11,7 +11,7 @@ pub struct ParametersValues {
     pub sar: f64,
     pub shape: f64,
     pub infection_duration: f64,
-    pub between_hh_transmission_reduction: f64,
+    pub between_hh_transmission_rr: f64,
     pub output_dir: String,
     pub data_dir: String,
 }
diff --git a/examples/network-hhmodel/seir.rs b/examples/network-hhmodel/seir.rs
index 735aba3b..36cdb939 100644
--- a/examples/network-hhmodel/seir.rs
+++ b/examples/network-hhmodel/seir.rs
@@ -2,7 +2,7 @@ use std::collections::HashSet;
 
 use ixa::log::info;
 use ixa::prelude::*;
-use ixa::{impl_property, ExecutionPhase, HashSet, HashSetExt};
+use ixa::{impl_property, ExecutionPhase};
 use rand_distr::Gamma;
 use serde::{Deserialize, Serialize};
 
@@ -158,11 +158,7 @@ mod tests {
 
         network::init(&mut context, 1.0);
 
-        let mut to_infect = Vec::<PersonId>::new();
-        context.with_query_results(with!(Person, Id(71)), &mut |people| {
-            to_infect.extend(people);
-        });
-
+        let to_infect = context.query(with!(Person, Id(71))).into_iter().collect();
         init(&mut context, &to_infect, 1.0);
 
         context.execute();

From 67fe36f6c530cf9d27e5cb6cd0b81583d99b8a4e Mon Sep 17 00:00:00 2001
From: Scott Olesen <ulp7@cdc.gov>
Date: Wed, 29 Apr 2026 11:18:19 -0400
Subject: [PATCH 05/10] docs: Network example: Implement Hash for RR (#864)

* docs: Network example: Implement Hash for RR
* Clarify the setup
---
 examples/network-hhmodel/README.md     |  2 ++
 examples/network-hhmodel/network.rs    | 34 +++++++++++++++++++++-----
 examples/network-hhmodel/parameters.rs |  1 +
 3 files changed, 31 insertions(+), 6 deletions(-)

diff --git a/examples/network-hhmodel/README.md b/examples/network-hhmodel/README.md
index d920f51a..b82c26b6 100644
--- a/examples/network-hhmodel/README.md
+++ b/examples/network-hhmodel/README.md
@@ -23,6 +23,8 @@ The simulation runs via:
   by whom during the simulation and saves the information to a csv in an `\output`
   folder.
 
+Note that the relative rate of transmission between households (relative to within households) is a property of the network edges. For technical reasons, ixa properties must implement `Eq`, which Rust floats do not. This example manually implements equality logic; future ixa versions may have other solutions.
+
 ## How to run the model
 
 `cargo run --example network-hhmodel`
diff --git a/examples/network-hhmodel/network.rs b/examples/network-hhmodel/network.rs
index 65b2f493..f4cf0b92 100644
--- a/examples/network-hhmodel/network.rs
+++ b/examples/network-hhmodel/network.rs
@@ -1,14 +1,36 @@
+use std::hash::{Hash, Hasher};
+
 use ixa::prelude::*;
 use ixa::{HashSet, HashSetExt};
 use rand_distr::Bernoulli;
+use serde::Serialize;
 
 use crate::loader::{open_csv, HouseholdId, Id};
 use crate::parameters::Parameters;
 use crate::{Person, PersonId};
 
+// ixa properties must implement `Eq` and `Hash`, but `f64`
+// does not. This example manually implements that logic manually.
+#[derive(Copy, Clone, Serialize, Debug)]
+pub struct FloatEq(f64);
+
+impl PartialEq for FloatEq {
+    fn eq(&self, other: &Self) -> bool {
+        (self.0.is_nan() && other.0.is_nan()) || (self.0 == other.0)
+    }
+}
+
+impl Hash for FloatEq {
+    fn hash<H: Hasher>(&self, state: &mut H) {
+        self.0.to_bits().hash(state);
+    }
+}
+
+impl Eq for FloatEq {}
+
 define_entity!(Edge);
 // relative transmission rate
-define_property!(struct RR(f64), Edge);
+define_property!(struct RR(FloatEq), Edge);
 define_property!(struct Node1(PersonId), Edge);
 define_property!(struct Node2(PersonId), Edge);
 
@@ -83,7 +105,7 @@ pub fn get_contacts(context: &Context, person_id: PersonId, duration: f64) -> Ha
     // duration, with a certain probability
     let mut contacts = HashSet::new();
     for edge in context.query(with!(Edge, Node1(person_id))) {
-        let RR(rr) = context.get_property(edge);
+        let RR(FloatEq(rr)) = context.get_property(edge);
         let Node2(person2) = context.get_property(edge);
         if context.sample_distr(NetworkRng, Bernoulli::new(base_p * rr).unwrap()) {
             contacts.insert(person2);
@@ -94,14 +116,14 @@ pub fn get_contacts(context: &Context, person_id: PersonId, duration: f64) -> Ha
 }
 
 pub fn init(context: &mut Context, between_hh_transmission_reduction: f64) {
-    // relative risk of transmission between (vs. within) households
+    // relative rate of transmission between (vs. within) households
     let rr = 1.0 / between_hh_transmission_reduction;
 
     // Create dense household networks
-    create_household_networks(context, RR(1.0));
+    create_household_networks(context, RR(FloatEq(1.0)));
     // Add other edges from csv's with lower transmission rate
-    load_edge_list(context, "AgeUnder5Edges.csv", RR(rr));
-    load_edge_list(context, "Age5to17Edges.csv", RR(rr));
+    load_edge_list(context, "AgeUnder5Edges.csv", RR(FloatEq(rr)));
+    load_edge_list(context, "Age5to17Edges.csv", RR(FloatEq(rr)));
 }
 
 #[cfg(test)]
diff --git a/examples/network-hhmodel/parameters.rs b/examples/network-hhmodel/parameters.rs
index f5ff0b52..0d8c94cf 100644
--- a/examples/network-hhmodel/parameters.rs
+++ b/examples/network-hhmodel/parameters.rs
@@ -11,6 +11,7 @@ pub struct ParametersValues {
     pub sar: f64,
     pub shape: f64,
     pub infection_duration: f64,
+    // relative rate of transmission
     pub between_hh_transmission_rr: f64,
     pub output_dir: String,
     pub data_dir: String,

From 434ec2a0f740d4ae9be16f1bceba49e63dec0240 Mon Sep 17 00:00:00 2001
From: Scott Olesen <ulp7@cdc.gov>
Date: Wed, 29 Apr 2026 11:20:03 -0400
Subject: [PATCH 06/10] fixup

---
 examples/network-hhmodel/seir.rs | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/examples/network-hhmodel/seir.rs b/examples/network-hhmodel/seir.rs
index 36cdb939..22191ed5 100644
--- a/examples/network-hhmodel/seir.rs
+++ b/examples/network-hhmodel/seir.rs
@@ -1,8 +1,6 @@
-use std::collections::HashSet;
-
 use ixa::log::info;
 use ixa::prelude::*;
-use ixa::{impl_property, ExecutionPhase};
+use ixa::{impl_property, ExecutionPhase, HashSet, HashSetExt};
 use rand_distr::Gamma;
 use serde::{Deserialize, Serialize};
 

From 91cbda6a0906df49eda239c3a0f22963e24f9da4 Mon Sep 17 00:00:00 2001
From: Scott Olesen <ulp7@cdc.gov>
Date: Wed, 29 Apr 2026 11:25:58 -0400
Subject: [PATCH 07/10] Use relative rate, not "reduction"

---
 examples/network-hhmodel/config.json | 2 +-
 examples/network-hhmodel/network.rs  | 6 ++----
 2 files changed, 3 insertions(+), 5 deletions(-)

diff --git a/examples/network-hhmodel/config.json b/examples/network-hhmodel/config.json
index b3b0deee..e7bd6b0d 100644
--- a/examples/network-hhmodel/config.json
+++ b/examples/network-hhmodel/config.json
@@ -5,7 +5,7 @@
     "sar": 0.15,
     "shape": 15.0,
     "infection_duration": 5.0,
-    "between_hh_transmission_reduction": 3.0,
+    "between_hh_transmission_reduction": 0.333,
     "output_dir": "examples/network-hhmodel/output",
     "data_dir": "examples/network-hhmodel/data"
   }
diff --git a/examples/network-hhmodel/network.rs b/examples/network-hhmodel/network.rs
index f4cf0b92..2d8570e3 100644
--- a/examples/network-hhmodel/network.rs
+++ b/examples/network-hhmodel/network.rs
@@ -115,10 +115,8 @@ pub fn get_contacts(context: &Context, person_id: PersonId, duration: f64) -> Ha
     contacts
 }
 
-pub fn init(context: &mut Context, between_hh_transmission_reduction: f64) {
-    // relative rate of transmission between (vs. within) households
-    let rr = 1.0 / between_hh_transmission_reduction;
-
+// `rr`: relative rate of transmission between (vs. within) households
+pub fn init(context: &mut Context, rr: f64) {
     // Create dense household networks
     create_household_networks(context, RR(FloatEq(1.0)));
     // Add other edges from csv's with lower transmission rate

From a7fd7e689b161eba69d7fba6788299631fa51412 Mon Sep 17 00:00:00 2001
From: Scott Olesen <ulp7@cdc.gov>
Date: Wed, 29 Apr 2026 11:41:47 -0400
Subject: [PATCH 08/10] fixup

---
 examples/network-hhmodel/config.json | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/examples/network-hhmodel/config.json b/examples/network-hhmodel/config.json
index e7bd6b0d..6be2c5c8 100644
--- a/examples/network-hhmodel/config.json
+++ b/examples/network-hhmodel/config.json
@@ -5,7 +5,7 @@
     "sar": 0.15,
     "shape": 15.0,
     "infection_duration": 5.0,
-    "between_hh_transmission_reduction": 0.333,
+    "between_hh_transmission_rr": 0.333,
     "output_dir": "examples/network-hhmodel/output",
     "data_dir": "examples/network-hhmodel/data"
   }

From a1a6a5ab7d91ff59f5e982edc2b2bc89a4b7d837 Mon Sep 17 00:00:00 2001
From: Scott Olesen <ulp7@cdc.gov>
Date: Thu, 30 Apr 2026 11:15:20 -0400
Subject: [PATCH 09/10] Implement Hash for RR, not FloatEq

---
 examples/network-hhmodel/network.rs | 18 +++++++++---------
 1 file changed, 9 insertions(+), 9 deletions(-)

diff --git a/examples/network-hhmodel/network.rs b/examples/network-hhmodel/network.rs
index 2d8570e3..5fe4b644 100644
--- a/examples/network-hhmodel/network.rs
+++ b/examples/network-hhmodel/network.rs
@@ -12,25 +12,25 @@ use crate::{Person, PersonId};
 // ixa properties must implement `Eq` and `Hash`, but `f64`
 // does not. This example manually implements that logic manually.
 #[derive(Copy, Clone, Serialize, Debug)]
-pub struct FloatEq(f64);
+pub struct RR(f64);
 
-impl PartialEq for FloatEq {
+impl PartialEq for RR {
     fn eq(&self, other: &Self) -> bool {
         (self.0.is_nan() && other.0.is_nan()) || (self.0 == other.0)
     }
 }
 
-impl Hash for FloatEq {
+impl Hash for RR {
     fn hash<H: Hasher>(&self, state: &mut H) {
         self.0.to_bits().hash(state);
     }
 }
 
-impl Eq for FloatEq {}
+impl Eq for RR {}
 
 define_entity!(Edge);
 // relative transmission rate
-define_property!(struct RR(FloatEq), Edge);
+impl_property!(RR, Edge);
 define_property!(struct Node1(PersonId), Edge);
 define_property!(struct Node2(PersonId), Edge);
 
@@ -105,7 +105,7 @@ pub fn get_contacts(context: &Context, person_id: PersonId, duration: f64) -> Ha
     // duration, with a certain probability
     let mut contacts = HashSet::new();
     for edge in context.query(with!(Edge, Node1(person_id))) {
-        let RR(FloatEq(rr)) = context.get_property(edge);
+        let RR(rr) = context.get_property(edge);
         let Node2(person2) = context.get_property(edge);
         if context.sample_distr(NetworkRng, Bernoulli::new(base_p * rr).unwrap()) {
             contacts.insert(person2);
@@ -118,10 +118,10 @@ pub fn get_contacts(context: &Context, person_id: PersonId, duration: f64) -> Ha
 // `rr`: relative rate of transmission between (vs. within) households
 pub fn init(context: &mut Context, rr: f64) {
     // Create dense household networks
-    create_household_networks(context, RR(FloatEq(1.0)));
+    create_household_networks(context, RR(1.0));
     // Add other edges from csv's with lower transmission rate
-    load_edge_list(context, "AgeUnder5Edges.csv", RR(FloatEq(rr)));
-    load_edge_list(context, "Age5to17Edges.csv", RR(FloatEq(rr)));
+    load_edge_list(context, "AgeUnder5Edges.csv", RR(rr));
+    load_edge_list(context, "Age5to17Edges.csv", RR(rr));
 }
 
 #[cfg(test)]

From c8e61b832f4abb88ae2ec4618b55ffa524091bb4 Mon Sep 17 00:00:00 2001
From: Scott Olesen <ulp7@cdc.gov>
Date: Wed, 20 May 2026 17:18:27 -0400
Subject: [PATCH 10/10] Clarify relative rate

---
 examples/network-hhmodel/README.md           |  2 +
 examples/network-hhmodel/config.json         |  2 +-
 examples/network-hhmodel/incidence_report.rs |  2 +-
 examples/network-hhmodel/main.rs             |  3 +-
 examples/network-hhmodel/network.rs          | 63 ++++++++------------
 examples/network-hhmodel/parameters.rs       |  3 +-
 examples/network-hhmodel/seir.rs             |  4 +-
 7 files changed, 32 insertions(+), 47 deletions(-)

diff --git a/examples/network-hhmodel/README.md b/examples/network-hhmodel/README.md
index b82c26b6..d09af73a 100644
--- a/examples/network-hhmodel/README.md
+++ b/examples/network-hhmodel/README.md
@@ -10,6 +10,8 @@ There are three data files:
 - `AgeUnder5Edges.csv` contains the edges connecting those aged under 5.
 - `Age5to17Edges.csv` contains the edges connecting those aged 5-17.
 
+The parameter `sar` is the secondary attack rate within each household, used to compute the within-household transmission rate. The parameter `relative_rate` is the ratio of the transmission rates between versus within households; it should be less than one.
+
 The simulation runs via:
 
 - `parameters.rs` sets up global properties for the model.
diff --git a/examples/network-hhmodel/config.json b/examples/network-hhmodel/config.json
index 6be2c5c8..ea756525 100644
--- a/examples/network-hhmodel/config.json
+++ b/examples/network-hhmodel/config.json
@@ -5,7 +5,7 @@
     "sar": 0.15,
     "shape": 15.0,
     "infection_duration": 5.0,
-    "between_hh_transmission_rr": 0.333,
+    "relative_rate": 0.333,
     "output_dir": "examples/network-hhmodel/output",
     "data_dir": "examples/network-hhmodel/data"
   }
diff --git a/examples/network-hhmodel/incidence_report.rs b/examples/network-hhmodel/incidence_report.rs
index de8f6f99..b7d80472 100644
--- a/examples/network-hhmodel/incidence_report.rs
+++ b/examples/network-hhmodel/incidence_report.rs
@@ -124,7 +124,7 @@ mod test {
             sar: 1.0,
             shape: 15.0,
             infection_duration: 5.0,
-            between_hh_transmission_rr: 1.0,
+            relative_rate: 1.0,
             data_dir: output_dir.to_str().unwrap().to_string(),
             output_dir: output_dir.to_str().unwrap().to_string(),
         };
diff --git a/examples/network-hhmodel/main.rs b/examples/network-hhmodel/main.rs
index f4c0abfb..98556154 100644
--- a/examples/network-hhmodel/main.rs
+++ b/examples/network-hhmodel/main.rs
@@ -41,7 +41,7 @@ fn initialize(context: &mut Context) {
         .clone();
 
     // Load network
-    network::init(context, parameters.between_hh_transmission_rr);
+    network::init(context, parameters.relative_rate);
 
     // Initialize incidence report
     incidence_report::init(context).unwrap();
@@ -51,5 +51,4 @@ fn initialize(context: &mut Context) {
 
     #[allow(clippy::vec_init_then_push)]
     seir::init(context, &to_infect, 1.0);
-    context.execute();
 }
diff --git a/examples/network-hhmodel/network.rs b/examples/network-hhmodel/network.rs
index 5fe4b644..3be2456d 100644
--- a/examples/network-hhmodel/network.rs
+++ b/examples/network-hhmodel/network.rs
@@ -1,42 +1,23 @@
-use std::hash::{Hash, Hasher};
+use std::hash::Hash;
 
 use ixa::prelude::*;
 use ixa::{HashSet, HashSetExt};
 use rand_distr::Bernoulli;
-use serde::Serialize;
 
 use crate::loader::{open_csv, HouseholdId, Id};
 use crate::parameters::Parameters;
 use crate::{Person, PersonId};
 
-// ixa properties must implement `Eq` and `Hash`, but `f64`
-// does not. This example manually implements that logic manually.
-#[derive(Copy, Clone, Serialize, Debug)]
-pub struct RR(f64);
-
-impl PartialEq for RR {
-    fn eq(&self, other: &Self) -> bool {
-        (self.0.is_nan() && other.0.is_nan()) || (self.0 == other.0)
-    }
-}
-
-impl Hash for RR {
-    fn hash<H: Hasher>(&self, state: &mut H) {
-        self.0.to_bits().hash(state);
-    }
-}
-
-impl Eq for RR {}
-
 define_entity!(Edge);
-// relative transmission rate
-impl_property!(RR, Edge);
+define_property!(struct RelativeRate(f64), Edge, impl_eq_hash = both);
 define_property!(struct Node1(PersonId), Edge);
 define_property!(struct Node2(PersonId), Edge);
 
 define_rng!(NetworkRng);
 
-fn add_bidi_edge(context: &mut Context, p1: PersonId, p2: PersonId, rr: RR) {
+fn add_bidi_edge(context: &mut Context, p1: PersonId, p2: PersonId, relative_rate: f64) {
+    let rr = RelativeRate(relative_rate);
+
     context
         .add_entity(with!(Edge, Node1(p1), Node2(p2), rr))
         .unwrap();
@@ -45,7 +26,7 @@ fn add_bidi_edge(context: &mut Context, p1: PersonId, p2: PersonId, rr: RR) {
         .unwrap();
 }
 
-fn create_household_networks(context: &mut Context, rr: RR) {
+fn create_household_networks(context: &mut Context) {
     let mut households = HashSet::new();
     let people: Vec<PersonId> = context.query(with!(Person)).into_iter().collect();
 
@@ -62,7 +43,8 @@ fn create_household_networks(context: &mut Context, rr: RR) {
 
             for i in 0..(members.len() - 1) {
                 for j in (i + 1)..(members.len()) {
-                    add_bidi_edge(context, members[i], members[j], rr);
+                    // by definition, edge rates are measured relative to within-household rates
+                    add_bidi_edge(context, members[i], members[j], 1.0);
                 }
             }
         }
@@ -76,19 +58,20 @@ fn get_entity_id_by_data_id(context: &mut Context, id: u16) -> PersonId {
     v[0]
 }
 
-fn load_edge_list(context: &mut Context, file_name: &str, rr: RR) {
+fn load_edge_list(context: &mut Context, file_name: &str, relative_rate: f64) {
     let mut reader = open_csv(file_name);
 
     for result in reader.deserialize() {
         let record: (u16, u16) = result.expect("Failed to parse edge");
         let p1 = get_entity_id_by_data_id(context, record.0);
         let p2 = get_entity_id_by_data_id(context, record.1);
-        add_bidi_edge(context, p1, p2, rr);
+        add_bidi_edge(context, p1, p2, relative_rate);
     }
 }
 
-fn sar_to_beta(sar: f64, infectious_period: f64) -> f64 {
-    1.0 - (1.0 - sar).powf(1.0 / infectious_period)
+// Assuming that time moves in steps of duration, what is the per-step probability of transmission?
+fn sar_to_prob(sar: f64, infectious_period: f64, duration: f64) -> f64 {
+    1.0 - (1.0 - sar).powf(duration / infectious_period)
 }
 
 /// Get all the effective contacts a person will have over a certain duration
@@ -98,16 +81,20 @@ pub fn get_contacts(context: &Context, person_id: PersonId, duration: f64) -> Ha
         .unwrap()
         .clone();
 
-    // Base probability of contact during the duration. Note that this assumes that the duration is not too high!
-    let base_p = duration * sar_to_beta(parameters.sar, parameters.incubation_period);
+    // Base probability of transmission during the duration.
+    let base_prob = duration * sar_to_prob(parameters.sar, parameters.incubation_period, duration);
+    assert!(base_prob <= 1.0);
 
     // Find all the people this person has edges to. Those people are contacts in this
     // duration, with a certain probability
     let mut contacts = HashSet::new();
     for edge in context.query(with!(Edge, Node1(person_id))) {
-        let RR(rr) = context.get_property(edge);
+        let RelativeRate(relative_rate) = context.get_property(edge);
         let Node2(person2) = context.get_property(edge);
-        if context.sample_distr(NetworkRng, Bernoulli::new(base_p * rr).unwrap()) {
+        if context.sample_distr(
+            NetworkRng,
+            Bernoulli::new(base_prob * relative_rate).unwrap(),
+        ) {
             contacts.insert(person2);
         }
     }
@@ -116,12 +103,12 @@ pub fn get_contacts(context: &Context, person_id: PersonId, duration: f64) -> Ha
 }
 
 // `rr`: relative rate of transmission between (vs. within) households
-pub fn init(context: &mut Context, rr: f64) {
+pub fn init(context: &mut Context, relative_rate: f64) {
     // Create dense household networks
-    create_household_networks(context, RR(1.0));
+    create_household_networks(context);
     // Add other edges from csv's with lower transmission rate
-    load_edge_list(context, "AgeUnder5Edges.csv", RR(rr));
-    load_edge_list(context, "Age5to17Edges.csv", RR(rr));
+    load_edge_list(context, "AgeUnder5Edges.csv", relative_rate);
+    load_edge_list(context, "Age5to17Edges.csv", relative_rate);
 }
 
 #[cfg(test)]
diff --git a/examples/network-hhmodel/parameters.rs b/examples/network-hhmodel/parameters.rs
index 0d8c94cf..8e0b43ef 100644
--- a/examples/network-hhmodel/parameters.rs
+++ b/examples/network-hhmodel/parameters.rs
@@ -11,8 +11,7 @@ pub struct ParametersValues {
     pub sar: f64,
     pub shape: f64,
     pub infection_duration: f64,
-    // relative rate of transmission
-    pub between_hh_transmission_rr: f64,
+    pub relative_rate: f64,
     pub output_dir: String,
     pub data_dir: String,
 }
diff --git a/examples/network-hhmodel/seir.rs b/examples/network-hhmodel/seir.rs
index 22191ed5..3609187b 100644
--- a/examples/network-hhmodel/seir.rs
+++ b/examples/network-hhmodel/seir.rs
@@ -138,15 +138,13 @@ mod tests {
         context.init_random(42);
         loader::init(&mut context);
 
-        // set sar and between_hh_transmission_reduction to 1.0 so that
-        // beta is 1.0
         let parameters = ParametersValues {
             incubation_period: 8.0,
             infectious_period: 27.0,
             sar: 1.0,
             shape: 15.0,
             infection_duration: 5.0,
-            between_hh_transmission_rr: 1.0,
+            relative_rate: 0.5,
             data_dir: "examples/network-hhmodel/tests".to_owned(),
             output_dir: "examples/network-hhmodel/tests".to_owned(),
         };