Error using inline. Input must be a string.

Hi Everyone. I'm studying the steepest descend method and I have tried to compile this method for a function. The problem is that when I compile, the command window shows "Error using inline (line 51)Input must be a string." and I don't know what to do.

[Stephen23]

Inline functions are basically obsolete... you should be using function handles!

Answer 1

[Walter Roberson]

syms X
fprime = matlabFunction( diff(exp(-X)+X.^4', X) );

If you do not have the symbolic toolbox then diff() is entirely the wrong function to use, as diff() on a non-symbolic object X is X(2:end,:) - X(1:end-1,:) -- that is, numeric difference between adjacent elements.

If you do not have the symbolic toolbox then

fprime = @(X) -exp(-X) + 4.*X.^3;

would be the formula.

[Roberto Antonino Ruggeri]

Oh thank you so much Walter!!! Now it works!! Thank you!!