str2sym error

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?

Answer 1

[Voss]

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 = 

[Giorgos Minas]

This seems to work. Thanks. Much appreciated.

[Voss]

You're welcome! Any questions, let me know.

Answer 2

[Walter Roberson]

Work around:

symfun('force(t)', sym('t'))

or

syms force(t)