Reduce the numbers of inputs in a numerical function

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Antonio
Antonio 2012-5-17
Hi all, if I have a numerical function f(x,y,z), and given that in my program most of the time x and y are fixed, I would like to evaluate f for some values x_0 and y_0, retaining the z dependence. At the end I would like to have a numerical funcion g(z)=f(x_0,y_0,z).
Is this possible?
Thanks!

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回答（2 个）

Andrei Bobrov
Andrei Bobrov 2012-5-17
eg:
f = @(x,y,z)x+y+z
x_0 = 3; y_0 = 6;
g = @(z)f(x_0 ,y_0 ,z)
EDIT
>> g(5),g(9),g(13)
ans =
12
ans =
16
ans =
20
>>
ADD use SymbolicToolbox
syms x y z
f = x*y*z
f1 = subs(f,{x,y},{3,4})
g = matlabFunction(f1)
>> g(5),g(9),g(13)
ans =
60
ans =
108
ans =
156
>>
  2 个评论
Antonio
Antonio 2012-5-17
I'm sorry, I have not specified that I do not want to call f each time!
I think what i want could be done with symbolic function. e.g.
syms z
g=f(x_0,y_0,z)
then call g as a function of z. But I want to know if one can do this without the use of symbolic functions.
The point is that the function f is very demanding, so I want to avoid calling it every time.
Walter Roberson
Walter Roberson 2012-5-17
I would wrap a simplify() around the subs(). That gives the opportunity for MuPAD to recognize any special cases and to resolve values that have effectively become constants (e.g., for cos(0) emit 1).

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Sargondjani
Sargondjani 2012-5-17
use passing of parameters: function value=my_fun(x,y,z); end
then you make an anonymous function: x0=... y0=... my_fun_z=@(z)my_fun(x0,y0,z);
now you can evaluate by just giving the value for z. (note: if you change the value of x0 or y0 you have to do the "my_fun_z=... " again)
however if some calculations inside your function stay the same (independent of z) and these are very demanding then you should split the function in a part with and without z to save calculation time
  3 个评论
显示 1更早的评论
Antonio
Antonio 2012-5-17
Of course I could separate them, but this is so complicated that cannot be done in practice.
Sargondjani
Sargondjani 2012-5-17
if you can not or do not want to separate the parts, then it is impossible indeed... it might still be worth the effort to try.... sometimes things look more complicated than they are

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