Re: A general problem with numerical functions defined in a messy way
- To: mathgroup at smc.vnet.net
- Subject: [mg108708] Re: A general problem with numerical functions defined in a messy way
- From: Bill Rowe <readnews at sbcglobal.net>
- Date: Sun, 28 Mar 2010 04:08:42 -0500 (EST)
On 3/27/10 at 5:10 AM, rjovale at gmail.com (ValeX) wrote:
>let's say that i have a numerical function f[x] which is defined in
>a quite messy way. For example, it could be defined as a Module that
>contains If, Whiles, interpolation functions, Import, .. This
>function works well without any error if I simply evaluate it, for
>example if i write f[5] and hit the enter key.
>The (my) problem is that often when i plug such a function in other
>routines, like FindMinimum, i get all sorts of errors and it doesn't
>work. Is there a way to tell Mathematica to just compute f[x] and
>then use that result for other things?
No, this simply cannot be done with an arbitrary f[x].
Mathematica does both numerical computations and symbolic
computations. Some built-in functions will handle one but not
the other. You simply cannot feed say NIntegrate a symbolic
result and expect an answer.
But this doesn't mean a specific problem cannot be dealt with.
For example, FindMinimum has more than one way to search for the
minimum. Rather than doing
FindMinimum[f[x], x]
I could do
FindMinimum[f[x], {x, x1, x2}]
Using this last method, FindMinimum avoids taking derivatives.
That might just be the difference between finding the minimum of
a "messy" f[x] or not.