How can I remove parentheses in a symbolic expression and perform the operations for the coefficients?

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Zoltán Csáti 2014-3-15

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https://ww2.mathworks.cn/matlabcentral/answers/121653-how-can-i-remove-parentheses-in-a-symbolic-expression-and-perform-the-operations-for-the-coefficient

评论： Zoltán Csáti 2014-3-15

I cannot use parentheses and / operations in my code because PHClab can't interpret them. So I need to remove them. How can I make it? For example I have

x2/24 - x1/6 + (x1*x4)/8 + (2*x3)/15 - (11*x4)/120 - x5/14 + (5*x6)/56 + x7/2 - x8 + x9

and I need

0.04167*x2 - 0.1667*x1 + 0.125*x1*x4 + ... + x9

Thank you

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Azzi Abdelmalek 2014-3-15

If you remove the brackets, the expression will change

Zoltán Csáti 2014-3-15

在 MATLAB Online 中打开

Perhaps, but I can only remove the brackets if I convert the symbolic expression to a character array. I removed the parentheses so I got:

x2/24 - x1/6 + x1*x4/8 + 2*x3/15 - 11*x4/120 - x5/14 + 5*x6/56 + x7/2 - x8 + x9

What should I do next? How can I get from x2/24 to 0.04167*x2 ?

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Answer 1

Mischa Kim 2014-3-15

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编辑：Mischa Kim 2014-3-15

在 MATLAB Online 中打开

Zoltán, use the vpa command:

 syms x2 x1 x4 x3
 f = x2/24 - x1/6 + x1*x4/8 + 2*x3/15
 f =
 x2/24 - x1/6 + (2*x3)/15 + (x1*x4)/8
 vpa(f,5)  % the "5" denotes the number of significant digits
 ans =
 0.041667*x2 - 0.16667*x1 + 0.13333*x3 + 0.125*x1*x4

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Zoltán Csáti 2014-3-15

编辑：Zoltán Csáti 2014-3-15

在 MATLAB Online 中打开

...except one thing. some of the coefficients have the form:

1.0760050095961908208164032839825*10^(-82)

So vpa works well, but how can I turn from the scientific notation to the the standard notation (so that it does not contain parentheses)? 1.0760050095961908208164032839825e-82 would be correct.

Zoltán Csáti 2014-3-15