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