In the recitation to Lecture 16 Projection Matrices and Least Squares we are given A = [1 1;2 4;-1 1] and told that A' * A = [6 8;8 10], but I get [6, 8; 8, 18]. I suppose I'm stupid but I get this both by hand and using MatLab, so something is peculiar.

Question

In the recitation to Lecture 16 Projection Matrices and Least Squares we are given A = [1 1;2 4;-1 1] and told that A' * A = [6 8;8 10], but I get [6, 8; 8, 18]. I suppose I'm stupid but I get this both by hand and using MatLab, so something is peculiar.

fwizbang · Answer

I noticed that as well, you're not wrong. Apart from the technicality of being numerically correct, the basic least square procedure is correct.