From bug-octave-request at bevo dot che dot wisc dot edu  Fri Dec 15 12:16:13 2000
Subject: max_complex_arg
From: "John W. Eaton" <jwe at bevo dot che dot wisc dot edu>
To: Rolf Fabian <fabian at tu-cottbus dot de>
Cc: "'bug-octave UWISC'" <bug-octave at bevo dot che dot wisc dot edu>
Date: Fri, 15 Dec 2000 12:15:41 -0600

On 15-May-2000, Rolf Fabian <fabian at tu-cottbus dot de> wrote:

| Hi,
| 	-- Problem 1 --
| max( x ) with complex argument x seems to return max(abs(x))
| actually. If multiple elements with same absolute value are
| present, return depends on calling syntax:
| 
| A:)	max([1-i,1+i])
| 	ans = 1 - 1i
| B:)	max( 1-i,1+i )
| 	ans = 1 + 1i
| 
| Calling mode 'A' seems always to return SMALLEST (ROW)-INDEX occurence
| of multiple elements at same abs, whereas 'B' seems to prefer
| LAST occurence in variable arg list.
| 
| I expect both calling modes to return the same thing.

OK.  I've appended a patch (for the current CVS sources) that should
fix this (and, BTW, make it Matlab compatible).

| 	-- Problem 2 --
| The comparison operators '>' '<' etc. seem to simply NEGLECT
| the imaginary part if complex numbers involved:
| 
| :)	(1+i)>1
| 	ans = 0
| 
| :)	(1-i)>1
| 	ans = 0
| :)	max([1,1-i,1+i])
| 	ans = 1 - 1i
| 
| Logically, latest four lines represent a severe contradiction!

Perhaps, but I believe that this behavior is Matlab compatible (unless
it has changed in Maltab 6).  Isn't that what everyone wants?!  :-/

Sorry for the long delay.

jwe


2000-12-15  John W. Eaton  <jwe at bevo dot che dot wisc dot edu>

	* lo-mappers.cc (xmin (const Complex&, const Complex& y):
	If args are equal in magnitude, return first arg instead of
	second.


Index: lo-mappers.cc
===================================================================
RCS file: /usr/local/cvsroot/octave/liboctave/lo-mappers.cc,v
retrieving revision 1.15
diff -u -r1.15 lo-mappers.cc
--- lo-mappers.cc	1999/09/10 05:17:01	1.15
+++ lo-mappers.cc	2000/12/15 18:07:58
 at @ -315,13 +315,13 @@
 Complex
 xmin (const Complex& x, const Complex& y)
 {
-  return abs (x) < abs (y) ? x : (xisnan (x) ? x : y);
+  return abs (x) <= abs (y) ? x : (xisnan (x) ? x : y);
 }
 
 Complex
 xmax (const Complex& x, const Complex& y)
 {
-  return abs (x) > abs (y) ? x : (xisnan (x) ? x : y);
+  return abs (x) >= abs (y) ? x : (xisnan (x) ? x : y);
 }
 
 /*



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