# Minreal function difference between 2021a and 2021b

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Roberto Echeverria on 16 Feb 2022
Hello all,
i am trying to simplifiy the following transfer function
num= [0 2.326783565332 0.047642481534536 1.1320523206336 0.018636773326054 0.1736525620563 0.0018797084587909 0.0095824683611615 5.0490779499017e-05 0.0001278775430483 3.1601961291737e-07 -4.7792321851035e-08 4.7241839384478e-12 1.6520593468991e-16 -3.5261492799393e-35]
den=[1 0.16677519120767 0.49411474213873 0.072903194148789 0.077462329441744 0.0095429580373996 0.0043848511975007 0.00044880580115597 6.2185817443617e-05 5.5616071215642e-06 3.4904054871597e-08 -1.8966547971896e-09 -1.5452863299211e-11 -2.9766685962549e-15 4.4489378695401e-21]
In matlab 2021a with a tolerance of 0.005 i get:
num=[0 2.326783565332 0.0242847369269 0.29192839103876 -6.2309086400998e-20]
den = [1 0.15310693671003 0.13130203172257 0.012309590052138 9.2125282212156e-05]
While in matlab 2021b with the same tolerance i get:
num=[0 2.326783565332 0.041644199007858 1.1327911885271 0.015731663720654 0.17402398971009 0.0014368084118137 0.0096420548390914 2.6156798199821e-05 0.00013131681404352 -1.2992874796127e-08 -4.5425159381868e-13 9.6955289981649e-32]
den=[1 0.16403829533202 0.49402991560459 0.071610816843538 0.077446228810322 0.0093570713626183 0.0043874423008049 0.00044020501132602 6.2578618017865e-05 5.5506274585318e-06 4.249926757687e-08 8.1746675586304e-12 -1.2218020065151e-17]
There is quite a difference in order, but which one is the correct one? There is not any notice about changes in this function in the 2021b list of changes, or at least, i could not find anything.
Kind regards
Roberto

Paul on 17 Feb 2022
Running 2021b in the Answers facility yieds results that are very close to, but not exactlyl the same as, what you got in 2021a.
num= [0 2.326783565332 0.047642481534536 1.1320523206336 0.018636773326054 0.1736525620563 0.0018797084587909 0.0095824683611615 5.0490779499017e-05 0.0001278775430483 3.1601961291737e-07 -4.7792321851035e-08 4.7241839384478e-12 1.6520593468991e-16 -3.5261492799393e-35];
den= [1 0.16677519120767 0.49411474213873 0.072903194148789 0.077462329441744 0.0095429580373996 0.0043848511975007 0.00044880580115597 6.2185817443617e-05 5.5616071215642e-06 3.4904054871597e-08 -1.8966547971896e-09 -1.5452863299211e-11 -2.9766685962549e-15 4.4489378695401e-21];
format long e
[numr,denr] = minreal(num,den,0.005) % obsolete usage?
10 pole-zero(s) cancelled
numr = 1×5
0 2.326783565332000e+00 2.428473692692200e-02 2.919283910388171e-01 -6.230908640101220e-20
denr = 1×5
1.000000000000000e+00 1.531069367100458e-01 1.313020317225583e-01 1.230959005213707e-02 9.212528221215011e-05
I get these exact same results on my local installation (2021b, Update 2). Can you post the exact code you ran in 2021b?
Roberto Echeverria on 22 Feb 2022
Thank you very much Paul on taking the effort to confirm my theories. I think the only option to get a good answer would be to ask the official support from mathworks, as it looks to me that they forgot to fix the complete minreal function.
In my case, I will use my own approach because i need the caller function to be consistent between different versions.
Thanks again and kind regards
Roberto

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