Isolate Coefficients of Multivariate Linear Polynomial

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Reuvenk
Reuvenk 2012-6-17
Hi, I have a symbolic expression
eqn = r - 2*x +7/4
I would like to isolate the coefficients of the variables (x, r and y (y's coefficient is 0)). How do I do that? I've tried using coeffs but that only lets me specify one variable. It would also be ok if I got two vectors back:
[ -2 , 1 , 7/4]
[x , r , 1]
even if they don't include y. Thanks!

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采纳的回答

Alexander
Alexander 2012-6-18
If you know that you have only linear terms and only x, r, and y, you could use diff to get the coefficients:
syms x r y
eqn = r - 2*x +7/4;
[diff(eqn, x), diff(eqn, r), diff(eqn, y)]
This gives:
ans =
[ -2, 1, 0]
  1 个评论
Reuvenk
Reuvenk 2012-6-18
That doesn't give the independent term, but I can easily find that by subbing 0 for all of the variables. Thanks for the answer!

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更多回答（1 个）

Christopher Creutzig
syms x r
eqn = r - 2*x +7/4
coeffs(eqn, [x, r])
ans =
[ 7/4, 1, -2]
Note that coeffs returns the coefficients in increasing order and leaves out zeroes:
>> coeffs(7*x^2*r^2 + 6*x^2*r + 5*x^2 + 4*x*r^2 + 3*x*r + 2*r^2, [x, r])
ans =
[ 2, 3, 4, 5, 6, 7]

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