Fix bugs in PolynomialPathFitter related to the number of input coordinate samples

CHANGELOG.md

@@ -88,6 +88,7 @@ v4.6
   other path-based force elements dependent on a user-provided expression. (#4035)
 - Fixed a bug where `DeGrooteFregly2016Muscle::getBoundsNormalizedFiberLength()` was returning
   tendon force bounds rather than fiber length bounds. (#4040)
+- Fixed bugs in `PolynomialPathFitter` when too few coordinate samples were provided. (#4039)
 
 
 v4.5.1

OpenSim/Actuators/PolynomialPathFitter.cpp

@@ -170,6 +170,12 @@ void PolynomialPathFitter::run() {
             "Expected 'num_parallel_threads' to be between 1 and {}, but "
             "received {}.", std::thread::hardware_concurrency(),
             get_num_parallel_threads())
+    OPENSIM_THROW_IF_FRMOBJ(
+            static_cast<int>(values.getNumRows()) < get_num_parallel_threads(), 
+            Exception, "Expected the number of time points in the coordinate "
+            "values table to be greater than 'num_parallel_threads', but "
+            "received {} and {}, respectively.", 
+            values.getNumRows(), get_num_parallel_threads())
     log_info("Number of parallel threads = {}", get_num_parallel_threads());
 
     // Number of samples per frame.
@@ -662,7 +668,8 @@ TimeSeriesTable PolynomialPathFitter::sampleCoordinateValues(
     int timeIdx = 0;
     const auto& times = values.getIndependentColumn();
     TimeSeriesTable valuesSampled;
-    double dt = (times[1] - times[0]) / (get_num_samples_per_frame() + 2);
+    double dt = (times.size() < 2) ? 0.01 : 
+            (times[1] - times[0]) / (get_num_samples_per_frame() + 2);
     for (int i = 0; i < get_num_parallel_threads(); ++i) {
         int numTimeIndexes = outputs[i].nrow() / get_num_samples_per_frame();
         for (int j = 0; j < numTimeIndexes; ++j) {

OpenSim/Actuators/Test/testPolynomialPathFitter.cpp

@@ -57,8 +57,9 @@ namespace {
         return processor;
     }
 
-    TableProcessor createCoordinatesTable(bool correctLabel, bool addMetaData) {
-        SimTK::Vector column = SimTK::Test::randVector(100);
+    TableProcessor createCoordinatesTable(bool correctLabel, bool addMetaData,
+            int numRows = 100) {
+        SimTK::Vector column = SimTK::Test::randVector(numRows);
         std::vector<double> times;
         times.reserve(column.size());
         for (int i = 0; i < column.size(); ++i) {
@@ -130,3 +131,17 @@ TEST_CASE("Invalid configurations") {
             "Expected 'maximum_polynomial_order' to be at most 9"));
     }
 }
+
+TEST_CASE("Number of rows less than the number of threads") {    
+    int numAvailableThreads = std::thread::hardware_concurrency();
+    int numRows = (numAvailableThreads == 1) ? 1 : numAvailableThreads - 1;
+    CAPTURE(numAvailableThreads);
+    CAPTURE(numRows);
+
+    PolynomialPathFitter fitter;  
+    fitter.setModel(createHangingMuscleModel());
+    fitter.setCoordinateValues(createCoordinatesTable(true, true, numRows));
+    fitter.setNumParallelThreads(numAvailableThreads);
+    REQUIRE_THROWS_WITH(fitter.run(), ContainsSubstring(
+        "Expected the number of time points in the coordinate values table"));
+}