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