so lets say that we have {{1,a},{0,2}} = A so that A^TA = {{1,a},{0,2}} *{{1, 0}, {a, 2}} = {{1 + a^2, 2 a}, {2 a, 4}} which has eigen values 1/2 (5 + a^2 pm sqrt(9 + 10 a^2 + a^4)) so that the operator norm is sqrt of 1/2 (5 + a^2 + sqrt(9 + 10 a^2 + a^4)) = sqrt(5 + a^2 + sqrt(9 + 10 a^2 + a^4))/sqrt(2) which gives us the stretching power of A