Allow setting seed for frequency offsets

Addresses #714

src/main/java/com/conveyal/analysis/models/AnalysisRequest.java

@@ -55,6 +55,7 @@ public class AnalysisRequest {
     public float toLon;
     public int fromTime;
     public int monteCarloDraws = 200;
+    public boolean lockSchedules = false;
     public int toTime;
     public String transitModes;
     public float walkSpeed;
@@ -244,6 +245,7 @@ public void populateTask (AnalysisWorkerTask task, UserPermissions userPermissio
         task.cutoffsMinutes = cutoffsMinutes;
 
         task.logRequest = logRequest;
+        task.lockSchedules = lockSchedules;
 
         task.accessModes = getEnumSetFromString(accessModes);
         task.directModes = getEnumSetFromString(directModes);

src/main/java/com/conveyal/r5/profile/FastRaptorWorker.java

@@ -145,7 +145,7 @@ public FastRaptorWorker (TransitLayer transitLayer, AnalysisWorkerTask request,
         this.accessStops = accessStops;
         this.servicesActive  = transit.getActiveServicesForDate(request.date);
 
-        offsets = new FrequencyRandomOffsets(transitLayer);
+        offsets = new FrequencyRandomOffsets(transitLayer, request);
 
         // compute number of minutes for scheduled search
         nMinutes = request.getTimeWindowLengthMinutes();

src/main/java/com/conveyal/r5/profile/FrequencyRandomOffsets.java

@@ -1,5 +1,6 @@
 package com.conveyal.r5.profile;
 
+import com.conveyal.analysis.models.AnalysisRequest;
 import com.conveyal.r5.transit.TransitLayer;
 import com.conveyal.r5.transit.TripPattern;
 import com.conveyal.r5.transit.TripSchedule;
@@ -12,8 +13,6 @@
 import java.util.HashMap;
 import java.util.Map;
 
-import static com.google.common.base.Preconditions.checkElementIndex;
-import static com.google.common.base.Preconditions.checkNotNull;
 import static com.google.common.base.Preconditions.checkState;
 
 /**
@@ -44,13 +43,19 @@ public class FrequencyRandomOffsets {
     private final Map<TripSchedule, int[]> offsetsForTripSchedule = new HashMap<>();
 
     /** The mersenne twister is a higher quality random number generator than the one included with Java */
-    private MersenneTwister mt = new MersenneTwister();
+    private MersenneTwister mt;
 
-    public FrequencyRandomOffsets(TransitLayer data) {
+    public FrequencyRandomOffsets(TransitLayer data, ProfileRequest request) {
         this.data = data;
         if (!data.hasFrequencies) {
             return;
         }
+        if (request == null || !request.lockSchedules) {
+            this.mt = new MersenneTwister();
+        } else {
+            // Use a fixed seed for each origin
+            this.mt = new MersenneTwister((int) (request.fromLat * 1e9));
+        }
         // Create skeleton empty data structure with slots for all offsets that will be generated.
         for (int pattIdx = 0; pattIdx < data.tripPatterns.size(); pattIdx++) {
             TripPattern tp = data.tripPatterns.get(pattIdx);

src/main/java/com/conveyal/r5/profile/McRaptorSuboptimalPathProfileRouter.java

@@ -113,7 +113,7 @@ public McRaptorSuboptimalPathProfileRouter (TransportNetwork network, ProfileReq
         this.touchedPatterns = new BitSet(network.transitLayer.tripPatterns.size());
         this.patternsNearDestination = new BitSet(network.transitLayer.tripPatterns.size());
         this.servicesActive = network.transitLayer.getActiveServicesForDate(req.date);
-        this.offsets = new FrequencyRandomOffsets(network.transitLayer);
+        this.offsets = new FrequencyRandomOffsets(network.transitLayer, request);
         this.saveFinalStates = saveFinalStates;
         if (saveFinalStates) this.finalStatesByDepartureTime = new TIntObjectHashMap<>();
 
@@ -150,7 +150,8 @@ public Collection<McRaptorState> route () {
 
         // We start at end of time window and work backwards (which is what range-RAPTOR does, in case we
         // re-implement that here). We use a constrained random walk to choose which departure minutes to sample as we
-        // work backward through the time window.  According to others (Owen and Jiang?), this is a good way to reduce
+        // work backward through the time window.  According to Owen and Murphy (2019)
+        // https://www.jtlu.org/index.php/jtlu/article/view/1379), this is a good way to reduce
         // the number of samples without causing an issue with variance in results.  This value is the constraint
         // (upper limit) on the walk.
         // multiply by two because E[random] = 1/2 * max.
@@ -535,7 +536,7 @@ private Collection<McRaptorState> doPropagationToDestination(int departureTime)
     }
 
     private ArrayList<Integer> generateDepartureTimesToSample (ProfileRequest request) {
-        // See Owen and Jiang 2016 (unfortunately no longer available online), add between f / 2 and
+        // See Owen and Murphy 2019 (https://www.jtlu.org/index.php/jtlu/article/view/1379), add between f / 2 and
         // f + f / 2, where f is the mean step.
         int randomWalkStepMean = (request.toTime - request.fromTime) / request.monteCarloDraws;
         int randomWalkStepWidthOneSided = randomWalkStepMean / 2;

src/main/java/com/conveyal/r5/profile/ProfileRequest.java

@@ -123,6 +123,8 @@ public class ProfileRequest implements Serializable, Cloneable {
 
     /** the maximum number of options presented PER ACCESS MODE */
     public int limit;
+
+    public boolean lockSchedules = false;
 
     /** The modes used to access transit */
     @JsonSerialize(using = LegModeSetSerializer.class)

src/test/java/com/conveyal/r5/transit/FrequencyRandomOffsetsTest.java

@@ -69,7 +69,7 @@ public void testPhasing () {
         layer.tripPatterns.add(pattern2);
         layer.rebuildTransientIndexes();
 
-        FrequencyRandomOffsets fro = new FrequencyRandomOffsets(layer);
+        FrequencyRandomOffsets fro = new FrequencyRandomOffsets(layer, null);
         fro.randomize();
 
         // check that phasing is correct
@@ -136,7 +136,7 @@ public void testPhasingAtLastStop () {
         layer.tripPatterns.add(pattern2);
         layer.rebuildTransientIndexes();
 
-        FrequencyRandomOffsets fro = new FrequencyRandomOffsets(layer);
+        FrequencyRandomOffsets fro = new FrequencyRandomOffsets(layer, null);
         fro.randomize();
 
         // check that phasing is correct