Here, in paragraph Data compression, one can find this sentence:
This means that we have three vectors $v_i$, each of which has $15$ entries, three vectors $u_i$, each of which has $25$ entries, and three singular values $\sigma_i$. This implies that we may represent the matrix using only $123$ numbers rather than the $375$ that appear in the matrix.
Can anyone please explain where "$123$ numbers" come from? How do I get this dimension?
From the number of components in the given vectors and the number of singular values, $3\times15+3\times25+3=123$