T.Crane wrote: > Hi, > > OK, I'm trying to figure out how to use the ODE solver > (scipy.integrate.ode.ode).
You will get more help from the scipy-user list than you will here. http://www.scipy.org/Mailing_Lists > Here's what I'm doing (in iPython) > > y0 = [0,1,1] > dt = 0.01 > tEnd = 12 > t0 = 0 > Y = zeros([tEnd/dt, 3]) > > As an aside, I've used this assignment for Y in the past and it > worked. When I tried it this morning I got a TypeError and a message > saying I needed to use an integer. Well, the current behavior is correct. When you give us a float instead of an int for a dimension, we shouldn't guess what you want. Particularly, in this case, truncating is incorrect. I ran your code and eventually wound up with an IndexError because your iteration ran past the end of Y and T. > So, instead... > > Y = zeros([int(tEnd/dt), 3]) > T = zero([int(tEnd/dt)]) Also, a better way to do this is simply to leave these as lists and simply append to them. That way, you don't have to manage indices. > index = 0 > def foo(t,y): > dy = zeros([3]) > dy[0] = y[1]*y[2] > dy[1] = -y[0]*y[2] > dy[2] = -0.51*y[0]*y[1] > return dy > > r = ode(foo).set_integrator('vode').set_initial_value(y0,t0) > while r.successful() and r.t < tEnd: > r.integrate(r.t+dt) > Y[index] = r.y > T[index] = r.t > index += 1 > > As a further aside, this system of three coupled linear ODE's is from > an example in MATLAB's documentation on their function ode45, so I > know what I 'should' get. The while loop and call to ode is adapted > from scipy's (very limited) documentation on scipy.integrate.ode.ode. > > At the end of this while loop I've gotten a few different results > depending on what I have no idea. This morning another TypeError > exception was thrown, saying: > > TypeError: Array can not be safely cast to required type. > > Although, to be fair this is after the output from one iteration: > > array([0.01, 1. , 1. ]) > > So, clearly this isn't working right. Does anyone have any experience > using this function or anything they can contribute? I tried your example and it worked for me (after fixing the IndexError). Could you come to scipy-user with the complete code that you ran (the one above isn't the one you ran; there is at least one typo), and the full traceback of the error? -- Robert Kern "I have come to believe that the whole world is an enigma, a harmless enigma that is made terrible by our own mad attempt to interpret it as though it had an underlying truth." -- Umberto Eco -- http://mail.python.org/mailman/listinfo/python-list
