probt(x,df,nc) returns the value of the distribution
function of the t distribution with df degrees of freedom
and optional non-centrality parameter nc. If not specified,
nc=0. nc is the value of the mean. Examples:
y=probt(1.96,10);
z=probt(1.96,10,3);
Copyright © 1997 by Jerry Alan Veeh. All rights reserved.