plotm was created so you can stop doing things like this:
plot(M(1,:),M(2,:)) or plot3(M(1,:),M(2,:),M(3,:)).
and start doing things like this:
plotm(M)

plotm works by separating any matrix with two or more rows into vectors. The vectors are passed to plot for 2 x n and to plot3 for 3 x n. If no inputs have multiple rows, plotm calls plot.

Scalars and row vectors (including handles, Name/Value pairs, LineSpecs, etc.) are preserved and passed to the plotting functions. For example, plotm(M1,'or',M2,'xb').

The equivalent function for line, linem, is also included.