> If you can help identify what Matlab does in this situation, and what

> should be fixed and where, then maybe something can be done about it.

Running the same script in Matlab 2016b produces no errors and the

following output.

Note Octave output from cheby2 is a row vector, Matlab is a column. I

don't know if this matters. Matlab output follows. Octave 4.2.0,

signal pkg v.1.3.2 ouput shown below that.

-------------------------------------

Matlab 2016b

>> conf.stages=6;

>> conf.reject=40;

>> conf.fsamp=1000;

>> fpL=0.52915085925565918945068233369966;

>> fpH=491.55617297547132693580351769924;

>> [z,p,k]=cheby2(conf.stages,conf.reject,[fpL.*2 ./conf.fsamp,fpH.*2./conf.fsamp])

z =

-0.999905676503125 + 0.013734558486828i

-0.999905676503125 - 0.013734558486828i

-0.998687143937134 + 0.051224881988044i

-0.998687143937134 - 0.051224881988044i

-0.999296201278521 + 0.037511359750324i

-0.999296201278521 - 0.037511359750324i

0.999999629730721 + 0.000860545419704i

0.999999629730721 - 0.000860545419704i

0.999994843220577 + 0.003211468862567i

0.999994843220577 - 0.003211468862567i

0.999997236381365 + 0.002351006089707i

0.999997236381365 - 0.002351006089707i

p =

-0.983753121609877 + 0.071492541325641i

-0.983753121609877 - 0.071492541325641i

-0.961750098624975 + 0.051154896580545i

-0.961750098624975 - 0.051154896580545i

-0.949728425507133 + 0.018486078667500i

-0.949728425507133 - 0.018486078667500i

0.999127670635969 + 0.004543010951549i

0.999127670635969 - 0.004543010951549i

0.997640877892379 + 0.003321080212941i

0.997640877892379 - 0.003321080212941i

0.996785136655982 + 0.001214672037223i

0.996785136655982 - 0.001214672037223i

k =

0.896584733013338

>> [~, idx] = sort (real (z));

>> z = z(idx)

z =

-0.999905676503125 + 0.013734558486828i

-0.999905676503125 - 0.013734558486828i

-0.999296201278521 + 0.037511359750324i

-0.999296201278521 - 0.037511359750324i

-0.998687143937134 + 0.051224881988044i

-0.998687143937134 - 0.051224881988044i

0.999994843220577 + 0.003211468862567i

0.999994843220577 - 0.003211468862567i

0.999997236381365 + 0.002351006089707i

0.999997236381365 - 0.002351006089707i

0.999999629730721 + 0.000860545419704i

0.999999629730721 - 0.000860545419704i

--------------------------------------------------------------

Octave 4.2.0

>>pkg load signal

>> conf.stages=6;

>> conf.reject=40;

>> conf.fsamp=1000;

>> fpL=0.52915085925565918945068233369966;

>> fpH=491.55617297547132693580351769924;

>> [z,p,k]=cheby2(conf.stages,conf.reject,[fpL.*2 ./conf.fsamp,fpH.*2./conf.fsamp]);

>> z'

ans =

-0.998687143937134 - 0.051224881988043i

-0.999296201278521 - 0.037511359750325i

-0.999905676503125 - 0.013734558486826i

0.999999629730722 - 0.000860545419713i

0.999997236381364 - 0.002351006089708i

0.999994843220576 - 0.003211468862565i

0.999994843220576 + 0.003211468862565i

0.999997236381364 + 0.002351006089708i

0.999999629730722 + 0.000860545419685i

-0.999905676503125 + 0.013734558486826i

-0.999296201278521 + 0.037511359750325i

-0.998687143937134 + 0.051224881988043i

>> p'

ans =

0.999127670635973 - 0.004543010951549i

0.997640877892371 - 0.003321080212942i

0.996785136655987 - 0.001214672037224i

0.996785136655987 + 0.001214672037222i

0.997640877892375 + 0.003321080212938i

0.999127670635973 + 0.004543010951549i

-0.983753121609872 + 0.071492541325644i

-0.961750098624987 + 0.051154896580549i

-0.949728425507125 + 0.018486078667483i

-0.949728425507125 - 0.018486078667483i

-0.961750098624987 - 0.051154896580549i

-0.983753121609872 - 0.071492541325644i

>> k

k = 0.896584733013339

>> [~, idx] = sort (real (z));

>> z = z(idx)'

z =

-0.999905676503125 - 0.013734558486826i

-0.999905676503125 + 0.013734558486826i

-0.999296201278521 - 0.037511359750325i

-0.999296201278521 + 0.037511359750325i

-0.998687143937134 - 0.051224881988043i

-0.998687143937134 + 0.051224881988043i

0.999994843220576 - 0.003211468862565i

0.999994843220576 + 0.003211468862565i

0.999997236381364 - 0.002351006089708i

0.999997236381364 + 0.002351006089708i

0.999999629730722 - 0.000860545419713i

0.999999629730722 + 0.000860545419685i

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