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Unable to sort symbolic variables in matlab

Asked by Aftab Ahmed Khan on 24 Feb 2016
Latest activity Commented on by Aftab Ahmed Khan on 24 Feb 2016
There is a an issue in one section of my code. Let I have this symbolic equation. When i use the coeffs function like this it gives me the right coefficients and variables.
eq=(10219275*P10_10)/2097152 - P10_9/10 - P9_10/10
[a,b]=coeffs(eq);
a =
[ -1/10, 10219275/2097152, -1/10]
b =
[ P10_9, P10_10, P9_10]
but i want it to return me the variables and its coefficients in this order. How can i go about this rearrangement.
b =
[ P9_10, P10_9, P10_10]
Please help me.

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2 Answers

Answer by Star Strider
on 24 Feb 2016
 Accepted Answer

You can tell coeffs the order in which you want the coefficients returned:
syms P10_9 P10_10 P9_10
eq=(10219275*P10_10)/2097152 - P10_9/10 - P9_10/10
[a,b]=coeffs(eq, [P9_10, P10_9, P10_10])
a =
[ -1/10, -1/10, 10219275/2097152]
b =
[ P9_10, P10_9, P10_10]

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Show 1 older comment
How do you want them sorted? I don’t see a pattern.
Sort order is first by the number after 'P' and before the '_', and secondarily by the number after the '_'
Well, i have managed to do it in another way found on the internet. Thanks once again.

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Answer by Walter Roberson
on 24 Feb 2016

Use http://www.mathworks.com/matlabcentral/fileexchange/10959-sort-nat--natural-order-sort a "natural sort" on the output of symvar() to get the order you want to do the sorting in, and then pass the sorted result as the second parameter of coeffs

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