Collect function doesn't work as intended

2022 11 1
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更新时间：2022 11 1
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syms z w K
% Previous steps executed, expresion directly copied from workspace
GzSFDen = 1.0*z^2 + (0.36788*K - 1.3679)*z + 0.26424*K + 0.36788;
GzSFDen = vpa(GzSFDen)
GzSFDen = 
% Substitution of z with (w+1)/(w-1)
Gw = subs(GzSFDen,z,(w+1)/(w-1))
Gw = 
% Obtained answer, coefficient of w^2 should only be 31606 K
incorrect = collect(Gw,w)
incorrect = 
% Expected answer, numerically close, num and den divided by 5
% Manually obtained
correct = (6141*K*w^2 + (12642 - 4924*K)*w - 1217*K + 27358)/(10000*w^2 - 20000*w + 10000);
correct = collect(correct,w)
correct = 

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Torsten
Torsten 2022-11-1
编辑：Torsten 2022-11-1
The -1 comes from -1.3679*w^2 + 0.36788*w^2 (numerator of the third and fourth term of your sum). So it is correct.
Shouldn't it be canceled with the 1*w^2 from the (w+1)^2/(w-1)^2
Torsten
Torsten 2022-11-1
Ran in:
Ran in:
Almost. But
rest = 50000*(1 - 1.3679 + 0.36788);
equals
rest
rest = -1.0000
is there a way to avoid that? Or there is a way to get rid of small values?
Torsten
Torsten 2022-11-1
Sure.
Replace
GzSFDen = 1.0*z^2 + (0.36788*K - 1.3679)*z + 0.26424*K + 0.36788;
by
GzSFDen = 1.0*z^2 + (0.36788*K - 1.36788)*z + 0.26424*K + 0.36788;

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