The cpu time will be different between a matrix (x) a vector and a vector (x) a matrix.


proc iml ;
  nrow=4000;
  ncol=4000;

  x = j(nrow, ncol, 0);
  y = j(nrow, 1,0);
  call randgen(x, "Normal");
  call randgen(y, "Normal");
  t1=time();
  xy=x*y;
  diff_xy=time()-t1;
  t1=time();
  yx=(y`*x`)`;
  diff_yx=time()-t1;
  
  print diff_xy diff_yx ;     
quit;