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Re: How do I pass a value to a function called by ode45?
Posted:
Feb 7, 2013 11:08 AM


"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/parameterizingfunctions.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 gobetween for ODE45 and the f function, they will both be satisfied. The anonymous function IS that adapter/gobetween. 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



