adding a matrix layer to an already existing matrix

I want to add a layer to my 180x180 matrix, seen below. N is where I define the actual matrix in the code. I want to add a layer to make it a 3D matrix such that the second layer has a cell value of 0 at (90,90) and increases by 1 for increasing i and j indices, and decreases by 1 for decreasing i and j indices. So I am essentially setting up a cartesian coordinate plane with the second layer. so the index (91,90) should have a value of 1, (92,90) a value of 2, (89,90) a value of -1, (90,91) a value of 1, etc. Any ideas?

N1 = randi([1,500],45,45);
N2 = randi([25,1000],45,45);
N3 = randi([100,2200],45,45);
N4 = randi([5,700],45,45);
N5 = randi([100,500],45,45);
N6 = randi([800,3500],45,45);
N7 = randi([1000,10000],45,45);
N8 = randi([15,1000],45,45);
N9 = randi([250,900],45,45);
N10 = randi([5000,11000],45,45);
N11 = randi([1750,9000],45,45);
N12 = randi([25,890],45,45);
N13 = randi([2000,7500],45,45);
N14 = randi([200,2300],45,45);
N15 = randi([25,750],45,45);
N16 = randi([50,1323],45,45); 
N = [N1  N2  N3  N4;
     N5  N6  N7  N8;
     N9  N10 N11 N12;
     N13 N14 N15 N16];

Answer 1

[Stephen23]

M(:,:,2) = bsxfun(@plus,-89:90,(-89:90).');

[Andrew Poissant]

Thanks! Worked like a charm

[Stephen23]

My pleasure. PS: it would be better to create your matrix at once, rather than using numbered variables:

M = [randi([   1,  500],45,45),randi([  25, 1000],45,45),...
     randi([ 100, 2200],45,45),randi([   5,  700],45,45);...
     randi([ 100,  500],45,45),randi([ 800, 3500],45,45),...
     randi([1000,10000],45,45),randi([  15, 1000],45,45);...
     randi([ 250,  900],45,45),randi([5000,11000],45,45),...
     randi([1750, 9000],45,45),randi([  25,  890],45,45);...
     randi([2000, 7500],45,45),randi([ 200, 2300],45,45),...
     randi([  25,  750],45,45),randi([  50, 1323],45,45)];

[Andrew Poissant]

Thanks for the tip. Why is this better? The way I am doing it now helps me visualize the breakup of the matrix better. Does your way lead to faster computation or something?

[Stephen23]

Some reasons:

1. Each of those variables N1, N2, etc, gets used once and then just clutters up your memory (and workspace) unnecessarily. The values are probably stored twice in memory (although MATLAB is cunning sometimes...).
2. Often numbered variables lead to dynamic variable names (not in this case, but it really is best to avoid getting into that trap).
3. Code that is more generalized (i.e. does not rely on hard-coded numbers, etc) is easier to adapt and is more useful. A cell array might be useful for this case.

Code is always a compromise, so if visualizing is critical to getting it right then that is okay too. So my comment was not a critical point, unless you are really trying to be careful with memory and are working with large arrays (as some of us do).

[Andrew Poissant]

Thank you for the info, I will use your suggestions.