Date: Feb 7, 2013 11:08 AM Author: Steven Lord Subject: Re: How do I pass a value to a function called by ode45?

"Jeff " <spREMOVEHITSjeffAT@SIGNoptonline.net> wrote in message

news:kes0dn$arn$1@newscl01ah.mathworks.com...

> "Steven_Lord" <slord@mathworks.com> wrote in message

> <kerhrj$aeq$1@newscl01ah.mathworks.com>...

>>

>>

>> "Jeff " <spREMOVEHITSjeffAT@SIGNoptonline.net> wrote in message

>> news:kerh1u$72o$1@newscl01ah.mathworks.com...

>> > I want to pass a value (beta) to a function which I'm passing to ode45,

>> > but I can't quite fiigure out how to do it from the documentation. Here

>> > is the current function to be passed:

>>

>> These examples show two approaches of how to pass additional parameters

>> into the function called by FZERO; those same techniques work with ODE45.

>>

>> http://www.mathworks.com/help/matlab/math/parameterizing-functions.html

>>

>> --

>> Steve Lord

>> slord@mathworks.com

>> To contact Technical Support use the Contact Us link on

>> http://www.mathworks.com

>

> Unfortunately, I cannot use nested or anonymous functions. The functions

> I'm calling are in separate files. I cut down the example I typed in, but

> basically, it uses an if..elseif block to choose a function based on other

> parameters.

>

> I was able to make my sample work by adding a third parameter to the

> declaration of f and then using this call:

> [t_steps,s1]=ode45(@(t,y) f(t,y,beta), t_steps, s0, options);

This uses an anonymous function and will work as long as you've defined beta

before this ODE45 call.

> But I can't say I understand what it's doing. And I note that t and y are

> not given values anywhere before the @(t,y) part of that command. But the

> correct values are being passed into the function (at least the first

> time) and I'm getting the results I expect.

ODE45 requires the function that you pass into it as a function handle for

the first input to accept two input arguments.

Your function f requires three input arguments.

If we have a function that accepted the two input arguments from ODE45 and

passed them and another value into f, to serve as an adapter or go-between

for ODE45 and the f function, they will both be satisfied. The anonymous

function IS that adapter/go-between. The "@(t, y)" section of the anonymous

function indicates that it accepts two inputs (and so is a valid first input

for ODE45) and the "f(t, y, beta)" section calls f with three input

arguments (as it requires.)

--

Steve Lord

slord@mathworks.com

To contact Technical Support use the Contact Us link on

http://www.mathworks.com