 variable that reduces a
criterion (not necessarily the best one). It is important for that
function to search for variables in a reasonable order (first, the most
correlated with <code>y</code>), so you should use
<code>fast_forward</code> after <code>reduce_matrix</code> (you can set
<code>minpv = 1</code> if you do not want to remove any predictor, just
change the order). It is good idea to run <code>fast_forward</code> with
a criterion which does not have a heavy penalty for the size of a model,
so for 