This function can be used to produce a
normal probability plot (which is useful for checking the
normality of the data). It is called by the glmlab plotting
window, but can also be used outside of glmlab.
The general form of the command is npplot(y,s);
where y is the data and s is 0 to include
a dotted line corresponding to the standard normal distribution,
and is 1 too include a dotted line corresponding to a normal
distribution with the same mean and variance as the given data, y.
The Statistics Toolbox of MATLAB has its own function for plotting a normal probability plot.