Substituting code into function handle

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Matt
Matt 2012-6-20
Hi all. I have a variable myFormula that is a mathematical function of three symbolic variables, a, b, and c. For example, it may be the case that
myFormula = a^2 + b - c/2;
I need to pass this expression into a function handle (I think that is the term, at least), such that my desired result is
thisFunction = @(a,b,c) a^2 + b - c/2;
The problem is that, although myFormula always depends on a, b, and c, the relationship between these variables is arbitrary. To get around this, I have found that
thisFunction = @(a,b,c) subs(myFormula);
is a viable solution. However, thisFunction needs to be passed into ode45 (which constitutes many iterations), which causes subs() to be evaluated thousands of times, making things extremely slow. It seems like there should be a simple solution to this - any suggestions?

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Walter Roberson
Walter Roberson 2012-6-20
If your formula is in the form of a symbolic expression, as is implied by your use of subs(), then use matlabFunction() to convert the expression into a function handle.
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Matt
Matt 2012-6-20
Excellent, thanks Walter. Out of curiosity, are there any alternatives to matlabFunction() that I could look into for this situation?
Walter Roberson
Walter Roberson 2012-6-20
Not really, none that would not pretty much end up doing what matlabFunction() does.

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