7.7 Matrix Operators
  BASIC provides a special set of MAT statements for array
  computations. These statements enable you to add, subtract,
  and multiply matrices, and to assign values to elements. Note
  that if you specify an array without subscripts (for example,
  MAT A), the default is two dimensions.

  BASIC also provides matrix functions to transpose and invert
  matrices and to find the determinant of a matrix you invert.