Error using inline. Input must be a string.

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Roberto Antonino Ruggeri 2016-2-11

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编辑： Roberto Antonino Ruggeri 2016-2-13

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.

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Stephen23 2016-2-11

编辑：Stephen23 2016-2-11

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

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Answer 1

Walter Roberson 2016-2-11

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https://ww2.mathworks.cn/matlabcentral/answers/267752-error-using-inline-input-must-be-a-string#answer_209521

在 MATLAB Online 中打开

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.