How to use symbolic variables and functions (Syms) in a Simulink Matlab Function?

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Rakesh
Rakesh on 14 Sep 2014
Edited: Ali Sh on 22 Jul 2021
I would like to create a Symbolic function within a Simulink Matlab Function to solve the variables h and t1. Matlab produces error "The function 'syms' is not supported for standalone code generation. See the documentation for coder.extrinsic to learn how you can use this function in simulation." when I try to compile the Simulink Matlab function with the following code.
syms Eq1(h,t1);
Eq1(h,t1) = h*t1;
I tried adding "coder.extrinsic('syms')" at the top, as shown below, and this generated the error "Undefined function or variable 'h'."
coder.extrinsic('syms');
syms Eq1(h,t1);
Eq1(h,t1) = h*t1;
How do I use symbolic variables and functions (Syms) in a Simulink Matlab Function?

Accepted Answer

Denis Gurchenkov
Denis Gurchenkov on 26 Sep 2014
I think the only solution is to use the syms function inside a separate .m file and call that file as extrinsic.
Create a new .m file, e.g. solveSyms.m, put all your code there:
function out = solveSyms(in) % add necessary inputs and outputs
syms x y
f = x^2*y + 5*x*sqrt(y);
out = subs(f, x, in);
end
Now call this new file from the MATLAB Function block:
coder.extrinsic('solveSyms');
out = 0;
out = solveSyms(in);
I'm not very familiar with Symbolic Math toolbox, so you would need to correct the code above to use your equation. Also, read the doc for coder.extrinsic:
  6 Comments
Ali Sh
Ali Sh on 22 Jul 2021
In order to use the output of separate .m file in Simulink function, you have to change the type of function output to double. then, it'll work.
function out = solveSyms(in) % add necessary inputs and outputs
syms x y
f = x^2*y + 5*x*sqrt(y);
out = subs(f, x, in);
out = double(out);
end

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More Answers (2)

Andrew Reibold
Andrew Reibold on 26 Sep 2014
Edited: Andrew Reibold on 26 Sep 2014
Example equation: abs(x+1) + abs(5x-1) = 6
How to solve (Here, I look for real solutions specifically):
syms x real;
solve(abs(x+1)+abs(5*x-2)==6,x);
answer
ans =
7/6
-3/4

Walter Roberson
Walter Roberson on 30 Nov 2016
Possibly
coder.extrinsic('sym');
coder.extrinsic('symfun');
h = sym('h');
t1 = sym('t1')
EQ1 = symfun(h*t1, h, t1) ;
  1 Comment
Walter Roberson
Walter Roberson on 7 Sep 2017
Note that any of these solutions can only work for "Normal" mode or for "Acceleration" mode, and cannot be used for Rapid Acceleration mode or for code generation to target. No part of the symbolic toolbox can have code generated for it. The use of coder.extrinsic and similar gives a work-around only for Acceleration mode, as there is still a backing MATLAB for that mode.

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