MATLAB: Trying to get a symbolic derivative from a string that the user inputs

MATLABsymbolictoolbox

I'm using Matlab R2018a on a Mac. According to the toolbox installer, I have the Symbolic toolbox installed. I want to have the user input a string like "x*x+t*3" and have it take a symbolic derivative, putting it into a form that I can then pass to eval() (I'm coding a Halley's method code which requires taking several derivatives of a user-specified expression). I'm having a problem and I can't tell if it's because the toolbox isn't active somehow or if I'm doing it wrong. Here's what I see:

>> syms x t

>> s="x*x+t*3"

s =

"x*x+t*3"

>> diff(s)

Undefined function 'diff' for input arguments of type 'string'.

what am I doing wrong – how do I debug this?

Best Answer

Use str2sym:

https://www.mathworks.com/help/symbolic/str2sym.html

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Secondly, what you are trying to do can be done correctly using for loop but since, but here is a simple solution using arrayfun,

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Best Answer

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