invrnd.m running
ans =
n=2, avgerr=0 
ans =
n=2, rnderr=9.71445e-017 
ans =
n=4, avgerr=2.39808e-013 
ans =
n=4, rnderr=2.35922e-016 
ans =
n=8, avgerr=7.31534e-007 
ans =
n=8, rnderr=5.42968e-016 

Warning: Matrix is close to singular or badly scaled.
         Results may be inaccurate. RCOND = 1.902830e-018.
> In invrnd at 16
ans =
n=16, avgerr=237.479