This uses what Mathcad calls a Vector Field Plot. I begin by defining the indices m and n, and then the x and y values to be used. Thus x and y both go from -6 to 6.
Subscript notation is obtained by hitting the left bracket key.
The right arrow returns to regular position. Then we define a matrix Z of complex numbers. Here is the way I typed it. Again, left bracket creates subscript position, and right arrow gets out. When you leave the region the 1 will disappear, but on Mathcad the imaginary unit is always typed as 1i.