From bug-octave-request  Tue Jun 22 15:53:32 1993
Subject: strange error
From: A. Scottedward Hodel <Dr dot A dot Scottedward dot Hodel at eng dot auburn dot edu>
To: bug-octave
Date: Tue, 22 Jun 93 15:53:27 CDT

The m-files below behave quite strangely under octave:

The main routine sets up a Lyapunov equation; the lyap subroutine just tries
to evaluate argument dimensions.  In the file lyap.m, if the line marked 
"uncomment the next line" is uncommented, then a value of $X = 1$ is returned, 
but no disp statements after 'dimension check to start' are printed out.
If the line is left commented out, then 'error: X undefined' is printed
out.  I've tried this example both on a DELL '386 running Unix and on
the Sparc stations at Auburn.  Consistent behavior between them.

Judging from the Matlab output, I'd guess that octave elseif and matlab
elseif parse differently.

Some wise souls would call this a feature instead of a bug.

main.m:------------------------------------------------------------------
a = [1 2; 3 4]
b =[1 1; 1 1]
lyap(a,b)
disp('exiting mainroutine')

lyap.m:------------------------------------------------------------------
function X = lyap(A, B)
disp('lyap: enter')
C = B;
B = A';
[ma,na] = size(A)
[mb,nb] = size(B)
[mc,nc] = size(C)

%uncomment the next line to get rid of the error
%X = 1;

disp('dimension check to start:')
if( (ma ~= na) | (mb ~= nb) | (mc ~= ma) | (nc ~= mb))
	disp('illegal dimensions')
	X = 2;
%	error('Dimensions do not agree.')
elseif (ma==0)
	disp('ma is 0')
	X = 3;
	return 
	end
end
disp('end of lyap; never printed out')
X = [];


Matlab output: (with the line commented out)
>> main

a =

     1     2
     3     4


b =

     1     1
     1     1

lyap: enter

ma =

     2


na =

     2


mb =

     2


nb =

     2


mc =

     2


nc =

     2

dimension check to start:
end of lyap; never printed out

ans =

     []

exiting mainroutine