Collect function doesn't work as intended

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 = 

[Torsten]

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.

[Cesar Adolfo Cruz Vargaya]

Shouldn't it be canceled with the 1*w^2 from the (w+1)^2/(w-1)^2

[Torsten]

Almost. But

rest = 50000*(1 - 1.3679 + 0.36788);

equals

rest

rest = -1.0000

[Cesar Adolfo Cruz Vargaya]

is there a way to avoid that? Or there is a way to get rid of small values?

[Torsten]

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;