The same concept holds for multidimensional lists, but care must be taken that the list indices do not interfere, best by separating them with an underscore '_':

for i=1 to 12
  for j=1 to 12
    wrongmatrix(i)(j)=i*j
    rightmatrix(i)_(j)=i*j

Why is the first matrix wrong? Simply because the matrix elements 1,12 and 11,2 (like several others) map to the same variable name: wrongmatrix112. The underscore makes sure that the indices stay separated: rightmatrix1_12 and rightmatrix11_2 are indeed different names.

If you know the number of columns and rows in advance, you can use leading zeroes to avoid the underscore:

for i=01 to 12
  for j=01 to 12
    rightmatrix(i)(j)=i*j

In the above case, rightmatrix0112 and rightmatrix1102 correctly map to different variable names.