MATLAB: 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.

Best Answer

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.
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