```Date: Jan 5, 2013 2:17 AM
Author: R Martinez
Subject: Re: How to get the Real and Imaginary part of an expression

Eduardo,Two problems:(1) Mathematica does not know that s is a complex variable.(2) The functions Re[ ] and Im[ ] work only for numeric arguments.Try the following:-----Clear[s, z, w, x, y](w = 882.)/(s^2 + 2*z*w*s + w^2)f = % /. s -> x + I yComplexExpand[%]-----------HTH,RaulOn Jan 2, 2013, at 6:16 PM, Eduardo M. A. M. Mendes <emammendes@gmail.com> wrote:> Hello> > I need to extract the real and imaginary part of the following expression> > (w=882)/(s^2+2*z*w*s+w^2)> > where w and z are positive constants.  s is a complex variable.> > Applying Re and Im to the expression does not do much.   By hand, one can easily find them. > > What am I missing?> > many thanks> > Ed> > > --Boundary_(ID_rnQ7W0VSrA7Op0O/vuqrsw)Content-type: text/html; CHARSET=US-ASCIIContent-transfer-encoding: quoted-printable<html><head><meta http-equiv="Content-Type" content="text/html =charset=us-ascii"></head><body style="word-wrap: break-word; =-webkit-nbsp-mode: space; -webkit-line-break: after-white-space; =">Eduardo,<div><br></div><div>Two problems:</div><div><br></div><div>(1) =Mathematica does not know that s is a complex =variable.</div><div><br></div><div>(2) The functions Re[ ] and Im[ ] =work only for numeric arguments.</div><div><br></div><div>Try the =following:</div><div><br></div><div>-----</div><div><div style="margin: =0px; font-family: Helvetica; font-size: 16px; ">Clear[s, z, w, x, y]<br>(w = 882.)/(s^2 + 2*z*w*s + w^2)<br><br>f = % /. s -&gt; x + I y<br><br>ComplexExpand[%]</div><div style="margin: 0px; font-family: Helvetica; =font-size: 16px; "><br></div><div style="margin: 0px; font-family: =Helvetica; font-size: 16px; ">-----------</div><div style="margin: =0px; font-family: Helvetica; font-size: 16px; "><br></div><div =style="margin: 0px; font-size: 16px; font-family: Helvetica; =">HTH,</div><div style="margin: 0px; font-size: 16px; font-family: =Helvetica; "><br></div><div style="margin: 0px; font-size: 16px; =font-family: Helvetica; ">Raul</div><div style="margin: 0px; =font-size: 12px; font-family: Helvetica; "><br></div><div><div>On Jan 2, =2013, at 6:16 PM, Eduardo M. A. M. Mendes &lt;<a =href="mailto:emammendes@gmail.com">emammendes@gmail.com</a>&gt; =wrote:</div><br class="Apple-interchange-newline"><blockquote =type="cite">Hello<br><br>I need to extract the real and imaginary part =of the following =expression<br><br>(w=882)/(s^2+2*z*w*s+w^2)<br><br>where w and z are =positive constants. &nbsp;s is a complex variable.<br><br>Applying Re =and Im to the expression does not do much. &nbsp;&nbsp;By hand, one can =easily find them. <br><br>What am I missing?<br><br>many =thanks<br><br>Ed<br><br><br><br></blockquote></div><br></div></body></html=>=--Boundary_(ID_rnQ7W0VSrA7Op0O/vuqrsw)--
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