str2sym error

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Giorgos Minas
Giorgos Minas on 21 Feb 2024
Edited: Voss on 21 Feb 2024
When using the str2sym function for a particular string I get the following error.
>> str2sym('force(t)')
Error using str2sym
Unable to convert string to symbolic expression:
Invalid indexing or function definition. Indexing must follow MATLAB
indexing. Function arguments must be symbolic variables, and
function body must be sym expression.
There seems to be something special about the word “force” in Matlab because any misspelling of the word (e.g. str2sym('forcei(t)') ) and the error disappears.
It is essential to use the word "force" for the program I run and I cannot use another word.
This is reproduced in the online version of Matlab here https://matlab.mathworks.com, as well as my local Matlab 2023a.
Could you please help?

Accepted Answer

Voss
Voss on 21 Feb 2024
I get a different error:
try
S = str2sym('force(t)')
catch e
disp(e.message);
end
Unable to convert string to symbolic expression: Undefined function 'force' for input arguments of type 'sym'.
Anyway, here's a workaround:
S = str2sym('forces(t)');
S = subs(S,'forces','force')
S = 
  2 Comments
Giorgos Minas
Giorgos Minas on 21 Feb 2024
This seems to work. Thanks. Much appreciated.
Voss
Voss on 21 Feb 2024
Edited: Voss on 21 Feb 2024
You're welcome! Any questions, let me know.

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More Answers (1)

Walter Roberson
Walter Roberson on 21 Feb 2024
Work around:
symfun('force(t)', sym('t'))
or
syms force(t)

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