# Extracting coefficients of 'sinwt', 'coswt', sin2wt etc from a symbiolic expression.

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Yugal Gupta il 8 Ago 2021
Modificato: Walter Roberson il 12 Ago 2021
Hello,
I am having a mathmatical symbolic expression and want to extract the coefficient of 'sinwt', 'coswt', 'sin2wt' and so on.
For e.g. the expression is,
where, , and are symbolic variables. Now, is there anyway to get the coefficient of 'sinwt', 'coswt', 'cos3wt' etc. from this expression ? or in other words, is it possible to get the following desired output ?
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Walter Roberson il 9 Ago 2021
Ah... you can get there in a single step with
combine(y, 'sincos')

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### Risposte (1)

Gargi Patil il 12 Ago 2021
Hi,
My understanding is that you would like to extract the coefficients of a symbolic trigonometric expression. The function "coeffs" can be used to return coefficients of an expression with respect to a specified term as follows:
syms a b c x
expr = a*sin(x)*b*sin(2*x) + c*sin(x);
[csin, tsin] = coeffs(expr, [sin(x), sin(2*x)])
csin =
tsin =
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Walter Roberson il 12 Ago 2021
Modificato: Walter Roberson il 12 Ago 2021
It turned out that they wanted the express rewritten in terms of cos(), and were not looking for coefficients such as you get with coeffs(); see https://www.mathworks.com/matlabcentral/answers/894797-extracting-coefficients-of-sinwt-coswt-sin2wt-etc-from-a-symbiolic-expression#comment_1679322

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