What is Matrix Rank?
The rank of a matrix is the maximum number of linearly independent rows (or columns). It equals the number of non-zero rows in row echelon form.
Properties:
- rank(A) ≤ min(rows, columns)
- Full rank means rank equals the smaller dimension
- Rank deficient means rank is less than the smaller dimension
- Zero matrix has rank 0
Applications:
- Linear Systems: Determines if Ax = b has solutions
- Nullity: nullity = n − rank (dimension of null space)
- Invertibility: Square matrix is invertible iff rank = n
- Span: Rank tells dimension of column/row space