CUR: Rebuilding a Matrix from Its Own Rows and Columns

Here is the four by four matrix from the book's example, with each entry as a bar. Its rank is two: row one is twice row zero, and row three is twice row zero plus row two.

Pick two rows and two columns. They form a cross in the matrix: C is the chosen columns, R the chosen rows, and where they meet, a two by two block.

The rest of the narration is in the book's Companion.