From bug-octave-request at bevo dot che dot wisc dot edu  Fri Dec 15 19:19:33 2000
Subject: c2d matched pole/zero equivalent.
From: "John W. Eaton" <jwe at bevo dot che dot wisc dot edu>
To: Ben Sapp <bsapp at lanl dot gov>
Cc: bug-octave at bevo dot che dot wisc dot edu
Date: Fri, 15 Dec 2000 19:19:25 -0600

On  7-Jun-2000, Ben Sapp <bsapp at lanl dot gov> wrote:

| Bug report for Octave from the CVS about a week ago configured for RedHat Linux
| 
| Description:
| -----------  
| The c2d function does not have the ability to use matched pole/zero equivalent
| for conversion.  
| 
| Fix:
| ---
| Apply the attached patch.   
| 
| The patch is not perfect in that it does not work on systems that
| are not SISO or purely continuous.  The books I have do not discuss
| how to handle MIMO systems.  If someone can suggest a place to read
| up on how to do this for MIMO and discrete/continuous systems I
| would do it.

Sorry for the long delay.

I made this change in the CVS sources.

Thanks,

jwe



| Index: c2d.m
| ===================================================================
| RCS file: /cvs/octave/scripts/control/system/c2d.m,v
| retrieving revision 1.3
| diff -u -r1.3 c2d.m
| --- c2d.m	2000/01/31 07:40:57	1.3
| +++ c2d.m	2000/06/07 14:31:34
|  at @ -33,7 +33,6 @@
|  ## use the matrix exponential (default)
|  ##  at item "bi"
|  ## use the bilinear transformation
| -##  at end table
|  ##  at example
|  ##     2(z-1)
|  ## s = -----
|  at @ -41,6 +40,13 @@
|  ##  at end example
|  ## FIXME: This option exits with an error if  at var{sys} is not purely
|  ## continuous. (The  at code{ex} option can handle mixed systems.)
| +##  at item "matched"
| +## use the matched pole/zero equivalent transformation 
| +##  at example
| +##  at end example      
| +## FIXME: IF the system is not SISO or purely continuous this option 
| +## exits with an error
| +##  at end table
|  ##  at item t
|  ## sampling time; required if sys is purely continuous.
|  ##
|  at @ -71,7 +77,7 @@
|  ## Created: October 1993
|  ## Updated by John Ingram for system data structure August 1996
|  
| -function dsys = c2d (sys, opt, T)
| +function dsys = myc2d (sys, opt, T)
|    ## parse input arguments
|    if(nargin < 1 | nargin > 3)
|      usage("dsys=c2d(sys[,T])");
|  at @ -99,7 +105,8 @@
|  
|    if (!is_sample(T))
|      error("sampling period T must be a postive, real scalar");
| -  elseif( ! (strcmp(opt,"ex") | strcmp(opt,"bi") ) )
| +  elseif( ! (strcmp(opt,"ex") | strcmp(opt,"bi") | \
| +	     strcmp(opt,"matched") ) )
|      error(["invalid option passed: ",opt])
|    endif
|  
|  at @ -167,6 +174,24 @@
|        D = d + (c*iab);
|        stnamed = strappend(stname,"_d");
|        dsys = ss2sys(A,B,C,D,T,0,rows(A),stnamed,inname,outname);
| +    endif
| +  elseif(strcmp(opt,"matched"))
| +    if(is_digital(sys))
| +      error("c2d: system is already digital");
| +    elseif((length(sys.inname) != 1) || (length(sys.outname) != 1))
| +      error("c2d: system in not single input, single output");
| +    else
| +      sys = sysupdate(sys,"zp");
| +      p = exp(sys.pol*T);
| +      z = exp(sys.zer*T);
| +      infinite_zeros = max(size(sys.pol))-max(size(sys.zer))-1;
| +      for i = 1:infinite_zeros
| +	z = [z ; -1];
| +      endfor
| +      ## Should the freaquency we adjust around always be 1?   
| +      [cmag,cphase,cw] = bode(sys,1);
| +      [dmag,dpahse,dw] = bode(zp2sys(z,p,1,T),1);
| +      dsys = zp2sys(z,p,cmag/dmag,T);
|      endif
|    else
|      error(["Bad option=",opt])

-- 
www.octave.org        | Thanking you in advance.  This sounds as if the
www.che.wisc.edu/~jwe | writer meant, "It will not be worth my while to
                      | write to you again."        -- Strunk and White



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