Chaops: now time can go backwards, but Frolic is not stable then.

src/chaos.hpp

@@ -179,10 +179,12 @@ namespace Sapphire
 
         void update(double dt)
         {
+            using namespace std;
+
             // If the derived class has informed us of a maximum stable time increment,
             // use oversampling to keep the actual time increment within that limit:
             // find the smallest positive integer n such that dt/n <= max_dt.
-            const int n = (max_dt <= 0.0) ? 1 : static_cast<int>(std::ceil(dt / max_dt));
+            const int n = (max_dt <= 0.0) ? 1 : static_cast<int>(ceil(abs(dt) / max_dt));
             const double et = dt / n;
             for (int i = 0; i < n; ++i)
                 step(et);