Why the plot generated with the spy command has a restrictive aspect ratio for long/tall matrices in R2021b?

When I create a SPY plot for a sparse matrix that has a lot more columns than rows, I get a plot which is very small and hard to use. For example if a matrix is of size 3 x 600, I get a plot similar to the following.

% Create random sparse matrix
z = rand(3,600);
z(z<.9) = 0;
z = sparse(z);
spy(z)

I cannot zoom in or expand the axes to see the structure in the matrix. 

How to enhance this plot?

Answer 1

[MathWorks Support Team]

SPY uses the size of the input matrix to adjust the plot box's aspect ratio. For tall or thin matrices, this gives you the behavior from your plot. Change the aspect ratio back to something closer to 1-to-1 to "undo" this.

spy(z); set(gca, 'PlotBoxAspectRatio', [1 1 1])

You can use this as a workaround. If you do, you're probably also going to want to adjust the marker size for the SPY plot a bit larger as well.