Confirmed.  Indeed your example from comment #2 is better.

The misleading example from comment #3 got truncated by good old Savannah. I received it via mail:

x = 0:2;
y = 0:3;
z = x' * y;
contour (x, y, z, 2:3)

error: __contour__: size of X must match number of columns in Z
error: called from
    __contour__ at line 88 column 9
    contour at line 74 column 18

Never mind. But I still do not see the documentation improvement nor understand the error you experienced.  Please can you give the exact sequence of commands that lead to your described error?

Please can you give the exact sequence of commands that lead to your described error?  I suspect you did not update all values properly when modifying "x".  The following works for me:

x = 0:2;      # [0   1   2]
y = x;        # [0   1   2]
z = x' * y

z =

   0   0   0
   0   1   2
   0   2   4

contour (x, y, z, 2:3) # works

and

x = 0:0.5:2;  # [0.00000    0.50000    1.00000    1.50000    2.00000]
y = x;        # [0.00000    0.50000    1.00000    1.50000    2.00000]
z = x' * y

z =

   0.00000   0.00000   0.00000   0.00000   0.00000
   0.00000   0.25000   0.50000   0.75000   1.00000
   0.00000   0.50000   1.00000   1.50000   2.00000
   0.00000   0.75000   1.50000   2.25000   3.00000
   0.00000   1.00000   2.00000   3.00000   4.00000

>> contour (x, y, z, 2:3)  # works

I do not understand what makes your example less error prone than the previous one.

x = 0:3;
y = x;
z = y' * x
z =

   0   0   0   0
   0   1   2   3
   0   2   4   6
   0   3   6   9

The matrix "z" to be plottet in your example will be square as well?