How to check if a user entered input will form a valid function handle?

The user enters a character vector (in the edit text field of Appdesigner). I want to convert it into a function handle. I am doing this by concatenating it with '@(x,y)', making the function compatible with matrices and then using str2func. However, I want to be able to check if the input by the user is valid. Also, the function entered by the user must have its variables as x and/or y only.

For example, if the entered input is 'log(x)+sin(y)' the entry is valid whereas if the input is 'log(x)+*sin(y)' it should show an error.

Thanks,

Mohit.

[Ameer Hamza]

Why 'log(x)+-sin(y)' is invalid? It is a valid MATLAB syntax.

[Mohit Kumar]

Okay, that was a poor mistake on my part. Something like log(x)+*sin(y). Have made the same change in the question.

Answer 1

[Ameer Hamza]

You may try exception handling to check if a function handle is valid

x = 'x^2+2+SUM(x)'; % SUM is not a valid function in MATLAB
f = str2func(['@(x) ' x]);

is_correct = true;
try
    f(0); % or some other value
catch ME
    is_correct = false;
    error(ME.message); % throw an error, remove this line if you don't
                       % want an error appearing in command window.
end

[Mohit Kumar]

Thanks! Seems to be working great as far I tested.

[Ameer Hamza]

I am glad to be of help! Let me know in the comment if there is some edge case where it fails.