OpenMP-enable the evaluation of a jacobian.

rpavlik · phkahler · commit 985e4fb67a96 · 2022-01-06T19:55:35.000-05:00
diff --git a/src/system.cpp b/src/system.cpp
@@ -84,11 +84,17 @@ void System::EvalJacobian() {
     mat.A.num.setZero();
     mat.A.num.resize(mat.m, mat.n);
 
-    std::vector<Eigen::Triplet<double>> values;
-    values.reserve(mat.A.sym.size());
-    for(const auto &exprTriplet : mat.A.sym) {
-        double value = exprTriplet.value()->Eval();
-        values.emplace_back(exprTriplet.row(), exprTriplet.col(), value);
+    std::vector<Eigen::Triplet<double>> values(mat.A.sym.size());
+    // Not using range-for to achieve (old) OpenMP compatibility:
+    // worth it because this profiles as taking a lot of time.
+    // Must be signed integer for MSVC.
+    const int n = (int)mat.A.sym.size();
+#pragma omp parallel for
+    for(int i = 0; i < n; ++i) {
+        const auto &exprTriplet = mat.A.sym[i];
+        double value            = exprTriplet.value()->Eval();
+        // assigning rather than emplace_back so we don't have to stick a critical pragma in here for openmp.
+        values[i] = {exprTriplet.row(), exprTriplet.col(), value};
     }
     mat.A.num.setFromTriplets(values.begin(), values.end());
 }
