Hi,
I'm having a problem in GAP when I attempt to assign entries
to lists. Apparently my problem is due to the way GAP makes
assignments. I've read the section on Lists in the GAP manual, but I
am still struggling to understand this. (I apologize in advance for
asking a question apparently covered in the manual!)

Explicitly -- I don't understand why the following loops give
different answers. The first example creates the array
[[1,2,3,4][5,6,7,8]] while the second does not.
Why?

(I am running GAP 4.1 on a Macintosh G3 laptop -- if that matters.)

----	GAP program ------------
#Filling in an array -- example 1
  mat := [[0,0,0,0], [0,0,0,0]];
  Print( mat, "\n" );
  entry := 0;
  for i1 in [1..2] do
  for i2 in [1..4] do
     entry := entry + 1;
     mat[i1][i2] := entry;
     mat2 := mat;
     Print( mat, "\n" );
  od; od;

Print("\n");

#Filling in an array -- example 2
  zero_1 := ListWithIdenticalEntries( 4, 0 );
  mat := ListWithIdenticalEntries( 2, zero_1 );
  Print( mat, "\n" );
  entry := 0;
  for i1 in [1..2] do
  for i2 in [1..4] do
     entry := entry + 1;
     mat[i1][i2] := entry;
     mat2 := mat;
     Print( mat, "\n" );
  od; od;
------

The real problem I am working on attempts to create
3-dimensional t x r x c arrays for various abelian groups of rank 3,
so the programming is more complicated than this simple example.
However, I think an explanation of this small example would be very
helpful.

Thanks,
Ken
-- 
Ken W. Smith, Professor of Mathematics, Central Michigan University
Phone: 517-774-6521; Fax: 517-774-2414; home phone: 772-5042.