How to generate t random numbers using Gauss

Here is a fast way to generate Student t random matrix with df degrees of freedom:

proc rndt(r,c,df);  /* r:rows, c:cols, df:df */
    local x,z;
    x = rndn(df,r*c);
    x = sumc(x.*x);
    x = reshape(x,r,c);
    z = rndn(r,c);
    retp(z./sqrt(x/df));
endp;
/* Example: y = rndt(100,5,2); */

Notes.

1. This is a procedure (almost) everybody knows. I just present it here for those who don't want to bother programming (like myself).
2. This procedure is fast because it does not operate element-wise.
3. You can make the procedure shorter by condensing multiple lines into one. For example,

   proc rndt(r,c,df);  /* r:rows, c:cols, df:df */
       retp(rndn(r,c)./sqrt(reshape(sumc(rndn(df,r*c).^2),r,c)/df));
   endp;
   

   The long proc is written longer than necessary in order to enhance readability.
4. You can easily modify it to use rndns instead of rndn.
5. The theory behind this procedure is this: Let X be chi-square(df) and Z be N(0,1), mutually independent. Then Z/(X/df)^1/2 is distributed as t with df degrees of freedom.