[Scilab-users] partial fractions

[Federico Miyara]

Dear All,

I'm wonderig whether there is a standard method to obtain the partial 
fraction expansion of a rational function.

Searching, I've found the function pfss(), which purportedly is meant 
for that, but I find it doesn't give a complete solution. For instance:

// Poles and zeros
p = [-8:-1];
z = [0 0 0 0];

// Numerator and denominator
N = prod(%s - z)
D = prod(%s - p)

// Rational function
H = N/D

// Partial fractions
HH = pfss(H)

The result is

HH  =
        HH(1)

    -8 -5.7428571s -3.9515873s² +0.2960317s³ -0.0946429s⁴ -0.006746s⁵ 
-0.0001984s⁶
------------------------------------------------------------------------------ 

               40320 +69264s +48860s² +18424s³ +4025s⁴ +511s⁵ +35s⁶ +s⁷

        HH(2)

    0.0001984
    ---------
      1 +s

The second component in the list is indeed one of the partial fractions, 
but the first one is not an irreductible version. Computing HH(1) + 
HH(2) yields H with good approximation.

I guess I could proceed iteratively with HH(1), but it would be nice to 
have a function performing this automatically. I couldn't find such a 
function

Regards,

Federico Miyara



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