Conversion from symbolic to matlabFunction and writing the result to a file

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Hello friends,
I have a simple problem but it seems difficult for me to fix. I want to create a matlabFunction from a symbolic vector and write that matlab function to a file. But, prior to converting the symbolic vector I have to do some manipulations to the symbolic vector. Let's take an example and you will see what I mean exactly. Consider the following symbolic vector f
syms Dm0 Ds0 Ds1 dt
f = [(2.*Dm0.*dt.^(1./2) - Ds0.*Ds1.*dt.^(1./2))./(2.*Ds0); 1; 0]
the problem is that the last 2 elements are not variables. So, if I type
matlabFunction(f,'File','fname','Vars',[Dm0,Ds0,Ds1,dt],'Outputs',{'EZ'});
then I get the following function
function EZ = fname(Dm0,Ds0,Ds1,dt)
%FNAME
% EZ = FNAME(DM0,DS0,DS1,DT)
% This function was generated by the Symbolic Math Toolbox version 8.6.
% 20-Jul-2022 16:21:27
t2 = sqrt(dt);
EZ = [(Dm0.*t2.*2.0-Ds0.*Ds1.*t2)./(Ds0.*2.0);1.0;0.0];
I am not happy with this since later I cannot do vector calculus due to the presence of constants. What I wish is to write the following matlab function to a file (I am not interested to just create the matlab function)
@(Dm0,Ds0,Ds1,dt)[(Dm0.*sqrt(dt).*2.0-Ds0.*Ds1.*sqrt(dt))./(Ds0.*2.0);1.0+0.*Ds0;0.*Ds0]
I can fix this problem by converting f to a character and then via character manipulations I can first create the character '[(Dm0.*sqrt(dt).*2.0-Ds0.*Ds1.*sqrt(dt))./(Ds0.*2.0);1.0+0.*Ds0;0.*Ds0]' and then apply char2func. But, the issue then would be that it just creates the matlab function and does not write it into a file (unfortunately, there is not a command like char2func(f,'File',filename,'Vars',[Dm0,Ds0,Ds1,dt],'Outputs',{'f'});.
Why I am interested to write the matlab function to a file? In reality my original symbolic vector f is extremely long. So, if I just turn it into a matlab function then matlabFunction does not optimize the code (so, later when I want to evaluate my matlab function its speed is low).
Any idea?
thanks in advance,
Babak

Answers (1)

Alan Weiss
Alan Weiss on 21 Jul 2022
Would it be possible to do the following: create a multiplier variable m in addition to the other variables?
syms Dm0 Ds0 Ds1 dt m
f = [(2.*Dm0.*dt.^(1./2) - Ds0.*Ds1.*dt.^(1./2))./(2.*Ds0); 1 + m*Ds0; m*Ds0]
f = 
matlabFunction(f,'File','fname','Vars',[Dm0,Ds0,Ds1,dt,m],'Outputs',{'EZ'});
When it comes time to do stuff with f, you can set m = 0.
Alan Weiss
MATLAB mathematical toolbox documentation

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