wrote section on matrix algebra
wrote section on matrix inverses
wrote second review section of chapter 2
wrote section on lu decomp
wrote section on permutations and transpose
corrections to permutations.xml for latex compilation
wrote basic file structure for chapter 3
moved a file for better naming
wrote section 3.1 on subspaces
wrote section on nullspace
add file rank.xml for section 3.3 of workbook.
wrote sections 3.4 and review 3.5
Merge branch 'src' into src-better
correct last task of section 3.1