<div dir="ltr"><div class="gmail_extra">On Tue, Sep 24, 2013 at 2:50 PM, Alexandre Torres Porres <span dir="ltr"><<a href="mailto:porres@gmail.com" target="_blank">porres@gmail.com</a>></span> wrote:<br><div class="gmail_quote">
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr">one doubt emerges really soon anyway. Since they are complex (there are two coordinate numbers for each pole and zero) how do I get only one number by, for example, summing or multiplying one pole to the other? as in:<div class="im">
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<br></div><div><b style="font-family:arial,helvetica,sans-serif;font-size:12.800000190734863px">b1</b><span style="font-family:arial,helvetica,sans-serif;font-size:12.800000190734863px"> = -(P0 + P1)</span><br style="font-family:arial,helvetica,sans-serif;font-size:12.800000190734863px">
<b style="font-family:arial,helvetica,sans-serif;font-size:12.800000190734863px">b2</b><span style="font-family:arial,helvetica,sans-serif;font-size:12.800000190734863px"> = (P0*P1)</span><br></div></div></div></blockquote>
<div><br><div class="gmail_default" style="font-family:arial,helvetica,sans-serif">You don't, the coefficients can be complex too. However, I discovered that mirroring (*) every pole and zero results in just real values without imaginary part. I don't have any mathematical proof for this, but it probably wouldn't be too hard to find such.<br>
<br></div><div class="gmail_default" style="font-family:arial,helvetica,sans-serif">*) adding another pole/zero for each complex one, like z=-j if you already have a z=j.<br></div></div></div></div></div>