solve residue by matlab

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adrian zizo
adrian zizo 2015-3-24
评论： Star Strider 2015-3-24
plz help me ....
how can I solve this problem by using residue by matlab :
25cos(πz)/((2z+1)^2 (z-2)^2 )
plz help me .. thank u .

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回答（2 个）

Star Strider
Star Strider 2015-3-24
If you have the Symbolic Math Toolbox, use the partfrac funciton:
syms z
f = 25*cos(pi*z)/((2*z+1)^2 * (z-2)^2 );
pf = partfrac(f, z)
produces:
pf =
cos(pi*z)/(z - 2)^2 - (4*cos(pi*z))/(5*(z - 2)) + (8*cos(pi*z))/(5*(2*z + 1)) + (4*cos(pi*z))/(2*z + 1)^2
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adrian zizo
adrian zizo 2015-3-24
but when I enter : syms z
f = 25*cos(pi*z)/((2*z+1)^2 * (z-2)^2 );
pf = partfrac(f, z)
in matlab , matlab give me error ...my matlab version is R2010a
Star Strider
Star Strider 2015-3-24
According to the online documentation, partfrac was introduced in R2015a, so you wouldn’t have it in R2010a.
I posted the result as ‘pf’ in my Answer, so you have the result of the partfrac operation without having to have the function in your version.

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Konstantinos Sofos
Konstantinos Sofos 2015-3-24
I would suggest to use L'Hôpital's rule but you could use also the following Adaptive numerical limit (and residue) estimation
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adrian zizo
adrian zizo 2015-3-24
I want residue of complex numbers .. plz help me
Konstantinos Sofos
Konstantinos Sofos 2015-3-24
编辑：Konstantinos Sofos 2015-3-24
Have a look in the link that i attached you before...
for your given example
f = @(z) 25*cos(pi*z)./((2*z+1).^2 .* (z-2).^2 )

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