fixes #189

A bug introduced with the recent max_dt facility prevented the rosenbrock
controller to increase step size in most cases (if max_dt=0). This is fixed
now, and a regression test case has been added.

include/boost/numeric/odeint/stepper/rosenbrock4_controller.hpp

@@ -163,6 +163,8 @@ public:
             if( m_max_dt != static_cast<time_type>(0) )
             {
                 dt = detail::min_abs(m_max_dt, dt_new);
+            } else {
+                dt = dt_new;
             }
             m_last_rejected = false;
             return success;

test/regression/Jamfile.v2

@@ -26,5 +26,6 @@ test-suite "odeint"
      [ run regression_147.cpp ]
      [ compile regression_149.cpp : <cxxflags>-std=c++0x ]
      [ run regression_168.cpp ]
+     [ run regression_189.cpp ]
      : <testing.launcher>valgrind
      ;

test/regression/regression_189.cpp

@@ -0,0 +1,71 @@
+/*
+ 
+ [begin_description]
+ Test case for issue 189: 
+ Controlled Rosenbrock stepper fails to increase step size
+ [end_description]
+
+ Copyright 2016 Karsten Ahnert
+ Copyright 2016 Mario Mulansky
+
+ Distributed under the Boost Software License, Version 1.0.
+ (See accompanying file LICENSE_1_0.txt or
+ copy at http://www.boost.org/LICENSE_1_0.txt)
+ */
+ 
+#define BOOST_TEST_MODULE odeint_regression_189
+
+#include <boost/numeric/odeint.hpp>
+
+#include <boost/test/unit_test.hpp>
+#include <boost/phoenix/core.hpp>
+#include <boost/phoenix/operator.hpp>
+
+using namespace boost::numeric::odeint;
+namespace phoenix = boost::phoenix;
+
+typedef boost::numeric::ublas::vector< double > vector_type;
+typedef boost::numeric::ublas::matrix< double > matrix_type;
+
+struct stiff_system
+{
+    void operator()( const vector_type &x , vector_type &dxdt , double /* t */ )
+    {
+        dxdt[ 0 ] = -101.0 * x[ 0 ] - 100.0 * x[ 1 ];
+        dxdt[ 1 ] = x[ 0 ];
+    }
+};
+
+struct stiff_system_jacobi
+{
+    void operator()( const vector_type & /* x */ , matrix_type &J , const double & /* t */ , vector_type &dfdt )
+    {
+        J( 0 , 0 ) = -101.0;
+        J( 0 , 1 ) = -100.0;
+        J( 1 , 0 ) = 1.0;
+        J( 1 , 1 ) = 0.0;
+        dfdt[0] = 0.0;
+        dfdt[1] = 0.0;
+    }
+};
+
+
+BOOST_AUTO_TEST_CASE( regression_189 )
+{
+    vector_type x( 2 , 1.0 );
+
+    size_t num_of_steps = integrate_const( make_dense_output< rosenbrock4< double > >( 1.0e-6 , 1.0e-6 ) ,
+            std::make_pair( stiff_system() , stiff_system_jacobi() ) ,
+            x , 0.0 , 50.0 , 0.01 ,
+            std::cout << phoenix::arg_names::arg2 << " " << phoenix::arg_names::arg1[0] << "\n" );
+    // regression: number of steps should be 74
+    BOOST_CHECK_EQUAL( num_of_steps , 74 );
+    
+    vector_type x2( 2 , 1.0 );
+
+    size_t num_of_steps2 = integrate_const( make_dense_output< runge_kutta_dopri5< vector_type > >( 1.0e-6 , 1.0e-6 ) ,
+            stiff_system() , x2 , 0.0 , 50.0 , 0.01 ,
+            std::cout << phoenix::arg_names::arg2 << " " << phoenix::arg_names::arg1[0] << "\n" );
+    
+    BOOST_CHECK_EQUAL( num_of_steps2 , 1531 );
+}