problem with coeffs command

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Ali Kiral
Ali Kiral 2026-2-5，14:21
评论： Ali Kiral about 22 hours 前
I have a symbollic expression
5*w - 5*z - u*((603367941593515*x)/4503599627370496 - y/2) - v*(x/2 + (603367941593515*y)/4503599627370496) - 1/8
which I want to extract the coefficient of u from. But the coeff command gives an erroneous result:
ans =
5*w - 5*z - u*((603367941593515*x)/4503599627370496 - y/2) - v*(x/2 + (603367941593515*y)/4503599627370496) - 1/8
coeffs(ans,u)
ans =
[5*w - 5*z - v*(x/2 + (603367941593515*y)/4503599627370496) - 1/8, y/2 - (603367941593515*x)/4503599627370496]
The first 'ans' is a multilinear polynomial in x y z u v and w, so shouldn't this work as coeffs is for polynomials.

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Paul
Paul about 22 hours 前
Ran in:
syms w z u y v x
5*w - 5*z - u*((603367941593515*x)/4503599627370496 - y/2) - v*(x/2 + (603367941593515*y)/4503599627370496) - 1/8
ans = 
coeffs(ans,u).'
ans = 
The second term in the result is the coefficient of u and the first term is everything else.
Is that not the expected result?
  4 个评论
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Steven Lord
Steven Lord 13 minutes 前
Ran in:
The coeffs(ans, u) function essentially extracts the coefficients for the and terms.
That's true if called with two outputs. If not it returns them in the opposite order, and .
syms w z u y v x
expr = 5*w - 5*z - u*((603367941593515*x)/4503599627370496 - y/2) - v*(x/2 + (603367941593515*y)/4503599627370496) - 1/8;
oneOutput = coeffs(expr, u);
[twoOutputs, terms] = coeffs(expr, u);
isequal(oneOutput, twoOutputs) % false
ans = logical
0
isequal(flip(oneOutput), twoOutputs) % true
ans = logical
1
Ali Kiral
Ali Kiral about 4 hours 前
@Paul I didn't know this command also gives an output for the zeroth power of u. You're right.

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