From bug-octave-request at che dot utexas dot edu  Tue May 24 20:01:26 1994
Subject: Re: a(:,[]) = [] 
From: John Eaton <jwe at che dot utexas dot edu>
To: Ken Neighbors <wkn at leland dot Stanford dot EDU>
cc: bug-octave at che dot utexas dot edu (Octave Bug)
Date: Tue, 24 May 94 20:01:17 EDT

Ken Neighbors <wkn at leland dot Stanford dot EDU> wrote:

: Using an empty matrix as an index apparently isn't allowed in octave,
: but perhaps it should be (especially for compatability with MATLAB).

: octave:1> a = [1 2; 3 4];
: octave:2> a(:,[]) = []
: error: second matrix index is an empty matrix
: error: evaluating assignment expression near line 2, column 9

Please try the following patch.

It will actually make Octave accept a few more things than Matlab
does.  For example, Matlab doesn't seem to mind that your example
above doesn't really conform (the : stands for two elements in this
case, so the index is 2x0 while the RHS is 0x0) but it does complain
if you try a([],[]) = [], which seems really bizarre to me...

At some point I may actually fix Octave to ensure that assignments
with empty indices and empty right-hand sides actually do conform, but
if I do, I'll allow you to select how strict you want the check to be.

Thanks,

jwe

*** src/tc-assign.cc~	1.13	1994/05/17 20:14:06
--- src/tc-assign.cc	1994/05/25 00:31:35
***************
*** 182,187 ****
--- 202,209 ----
  	}
      }
  
+ // The do_matrix_assignment functions can't handle empty matrices, so
+ // don't let any pass through here.
    switch (nargs)
      {
      case 2:
***************
*** 189,196 ****
  	::error ("matrix index is null");
        else if (args[1].is_undefined ())
  	::error ("matrix index is undefined");
-       else if (args[1].is_empty ())
- 	::error ("matrix index is an empty matrix");
        else
  	do_matrix_assignment (rhs, args[1]);
        break;
--- 211,216 ----
***************
*** 201,210 ****
  	::error ("first matrix index is undefined");
        else if (args[2].is_undefined ())
  	::error ("second matrix index is undefined");
!       else if (args[1].is_empty ())
! 	::error ("first matrix index is an empty matrix");
!       else if (args[2].is_empty ())
! 	::error ("second matrix index is an empty matrix");
        else
  	do_matrix_assignment (rhs, args[1], args[2]);
        break;
--- 221,237 ----
  	::error ("first matrix index is undefined");
        else if (args[2].is_undefined ())
  	::error ("second matrix index is undefined");
!       else if (args[1].is_empty () || args[2].is_empty ())
! 	{
! 	  if (! rhs.is_empty ())
! 	    {
! 	      ::error ("in assignment expression, a matrix index is empty");
! 	      ::error ("but hte right hand side is not an empty matrix");
! 	    }
! // XXX FIXME XXX -- to really be correct here, we should probably
! // check to see if the assignment conforms, but that seems like more
! // work than it's worth right now...
! 	}
        else
  	do_matrix_assignment (rhs, args[1], args[2]);
        break;
***************
*** 221,230 ****
    int nr = rows ();
    int nc = columns ();
  
!   if (user_pref.do_fortran_indexing)
!     fortran_style_matrix_assignment (rhs, i_arg);
!   else if (nr <= 1 || nc <= 1)
!     vector_assignment (rhs, i_arg);
    else
      ::error ("single index only valid for row or column vector");
  }
--- 251,281 ----
    int nr = rows ();
    int nc = columns ();
  
!   if (user_pref.do_fortran_indexing || nr <= 1 || nc <= 1)
!     {
!       if (i_arg.is_empty ())
! 	{
! 	  if (! rhs.is_empty ())
! 	    {
! 	      ::error ("in assignment expression, matrix index is empty but");
! 	      ::error ("right hand side is not an empty matrix");
! 	    }
! // XXX FIXME XXX -- to really be correct here, we should probably
! // check to see if the assignment conforms, but that seems like more
! // work than it's worth right now...
! 
! // The assignment functions can't handle empty matrices, so don't let
! // any pass through here. 
! 	  return;
! 	}
! 
!       if (user_pref.do_fortran_indexing)
! 	fortran_style_matrix_assignment (rhs, i_arg);
!       else if (nr <= 1 || nc <= 1)
! 	vector_assignment (rhs, i_arg);
!       else
! 	panic_impossible ();
!     }
    else
      ::error ("single index only valid for row or column vector");
  }