determinant.kt

fun determinant(matrix: Matrix): Double {
  require(matrix.rows == matrix.cols)

  if (matrix.rows == 1) return matrix[0,0]
  if (matrix.rows == 2) return (
    matrix[0,0] * matrix[1,1] - 
    matrix[0,1] * matrix[1,0]
  )

  var det = 0.0
  for (c in 0 until matrix.cols) {
    var incValue = 1.0
    var decValue = 1.0

    for (r in 0 until matrix.rows) {
      incValue *= matrix[r, (c+r) % matrix.cols]
      decValue *= matrix[matrix.rows-r-1, (c+r) % matrix.cols]
    }
    det += (incValue - decValue)
  }
  return det
}