Hi Rick,

Regarding this statement:" The principal components of A.T * A are the columns of the V matrix; the scores are the columns of U":

1) Sometimes I'm very confused by the terminologies used by different authors. “principal components” and “scores” in this blog can be read as “principal axes/principal directions” and “principal components” respectively in other literature.

2) The V in A = U Σ V.T, is computed as the eigenvectors of A.T * A. so, the phrase “The principal components of A.T * A” might not be appropriate, since it is the principal components (or principal axes) for the data A itself.

3) The scores (or principal components used by other authors) are not the columns of U; they are columns of U * Σ or A*V if my memory serves me well …