How to take an equation as input from user and read the coefficient from it?

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Sourin Dey 2016-12-27

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https://ww2.mathworks.cn/matlabcentral/answers/318316-how-to-take-an-equation-as-input-from-user-and-read-the-coefficient-from-it

回答： Walter Roberson 2016-12-27

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KSSV 2016-12-27

What equation? Can you give an example?

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Answer 1

Walter Roberson 2016-12-27

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If you have the Symbolic toolbox, then you could convert the string representing the equation to a function handle using str2func() and then you could pass symbolic arguments to it to get a symbolic representation of it.

At that point, if the equation is known to represent a polynomial, then you can use coeffs() to get the coefficients.

If the equation is not known to represent a polynomial then you can use children() to break it into pieces, and examine the pieces using symvar() to determine whether they contain the variable of interest. However, in such a case it gets tricky to define what the coefficients are. For example, for sin(2*x) it is not really correct to say that the coefficient of x is 2.