def run_example(with_plots=True): """ The same as example :doc:`EXAMPLE_cvode_basic` but now integrated backwards in time. on return: - :dfn:`exp_mod` problem instance - :dfn:`exp_sim` solver instance """ #Define the rhs def f(t, y): ydot = -y[0] return N.array([ydot]) #Define an Assimulo problem exp_mod = Explicit_Problem( f, t0=5, y0=0.02695, name=r'CVode Test Example (reverse time): $\dot y = - y$ ') #Define an explicit solver exp_sim = CVode(exp_mod) #Create a CVode solver #Sets the parameters exp_sim.iter = 'Newton' #Default 'FixedPoint' exp_sim.discr = 'BDF' #Default 'Adams' exp_sim.atol = [1e-8] #Default 1e-6 exp_sim.rtol = 1e-8 #Default 1e-6 exp_sim.backward = True #Simulate t, y = exp_sim.simulate(0) #Simulate 5 seconds (t0=5 -> tf=0) #print 'y(5) = {}, y(0) ={}'.format(y[0][0],y[-1][0]) #Basic test nose.tools.assert_almost_equal(float(y[-1]), 4.00000000, 3) #Plot if with_plots: P.plot(t, y, color="b") P.title(exp_mod.name) P.ylabel('y') P.xlabel('Time') P.show() return exp_mod, exp_sim