Collect function doesn't work as intended

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评论： Torsten 2022-11-1

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 =

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

Torsten 2022-11-1

Sure.

Replace

GzSFDen = 1.0*z^2 + (0.36788*K - 1.3679)*z + 0.26424*K + 0.36788;

GzSFDen = 1.0*z^2 + (0.36788*K - 1.36788)*z + 0.26424*K + 0.36788;

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