Catch solver error (#152)

Author: mrp089

src/algebra/SparseSystem.cpp

@@ -100,6 +100,11 @@ void SparseSystem::update_jacobian(double time_coeff_ydot,
 
 void SparseSystem::solve() {
   solver->factorize(jacobian);
+  if (solver->info() != Eigen::Success) {
+    throw std::runtime_error(
+        "System is singular. Check your model (connections, boundary "
+        "conditions, parameters).");
+  }
   dydot.setZero();
   dydot += solver->solve(residual);
 }