Python-Math-Algorithms/matrix/__init__.py

import math


class Matrix:

    def __init__(self, rows, cols):
        self.rows = rows
        self.cols = cols

        self.fields = []

        # initialize to identity matrix
        for x in range(rows):
            row = []

            for y in range(cols):
                row.append(float(x == y))

            self.fields.append(row)

    def __str__(self):
        return self.fields.__str__()

    # convert this matrix to identity
    def to_identity(self):
        for x in range(self.rows):
            for y in range(self.cols):
                self.fields[x][y] = float(x == y)

    def transpose(self):
        result = Matrix(self.cols, self.rows)

        for x in range(self.rows):
            for y in range(self.cols):
                result.fields[y][x] = self.fields[x][y]

        return result

    def __mul__(self, other):
        result = Matrix(self.rows, other.cols)

        for x in range(self.rows):
            for y in range(other.cols):
                sum = 0

                for i in range(self.cols):
                    sum += self.fields[x][i] * other.fields[i][y]

                result.fields[x][y] = sum

        return result

    def scale(self, other):
        result = Matrix(self.rows, other.cols)

        for x in range(self.rows):
            for y in range(other.cols):

                result.fields[x][y] = self.fields[x][y] * other

        return result

    def __add__(self, other):
        result = Matrix(self.rows, self.cols)

        for x in range(self.rows):
            for y in range(self.cols):
                result.fields[x][y] = self.fields[x][y] + other.fields[x][y]

        return result

    def __sub__(self, other):
        result = Matrix(self.rows, self.cols)

        for x in range(self.rows):
            for y in range(self.cols):
                result.fields[x][y] = self.fields[x][y] - other.fields[x][y]

        return result

    def slice(self, row_min, row_max, col_min, col_max):
        rows = row_max - row_min
        cols = col_max - col_min

        result = Matrix(rows, cols)

        for x in range(row_min, row_max):
            for y in range(col_min, col_max):
                result.fields[x][y] = self.fields[x][y]

        return result

    def exclude_row_and_col(self, i):
        result = Matrix(self.rows - 1, self.cols - 1)

        for x in range(i):
            for y in range(i):
                result.fields[x][y] = self.fields[x][y]

        for x in range(i + 1, self.rows - 1):
            for y in range(i + 1, self.cols - 1):
                result.fields[x][y] = self.fields[x][y]

        return result

    def determinant(self):
        if self.rows == 2 and self.cols == 2:
            return self.fields[0][0] * self.fields[1][1] - self.fields[0][1] * self.fields[1][0]

        # Satz von Sarrus
        if self.rows == 3 and self.cols == 3:
            aei = self.fields[0][0] * self.fields[1][1] * self.fields[2][2]
            bfg = self.fields[0][1] * self.fields[1][2] * self.fields[2][0]
            cdh = self.fields[0][2] * self.fields[1][0] * self.fields[2][1]
            ceg = self.fields[0][2] * self.fields[1][1] * self.fields[2][0]
            afh = self.fields[0][0] * self.fields[1][2] * self.fields[2][1]
            bdi = self.fields[0][1] * self.fields[1][0] * self.fields[2][2]
            return aei + bfg + cdh - ceg - afh - bdi

        # Laplace
        if self.rows == self.cols:
            # perform laplace on 2nd row
            self.__laplace_row(1)

    def __laplace_row(self, i):
        sum = 0
        for i in range(self.rows):
            sum += math.pow(-1, i + 1) * self.exclude_row_and_col(i).determinant()

        return sum

    def cramer(self, vector, order):
        return Matrix.from_vector(vector, order).determinant() / self.determinant()

    @classmethod
    def from_array(cls, array):
        matrix = Matrix(rows=len(array), cols=len(array[0]))

        for y in range(matrix.cols):
            for x in range(matrix.rows):
                matrix.fields[x][y] = array[x][y]

        return matrix

    @classmethod
    def from_vector(cls, vector, column):
        matrix = Matrix(rows=len(vector), cols=len(vector))

        for y in range(matrix.rows):
            matrix.fields[y][column] = vector[y]

        return matrix

def test():
    mat1 = Matrix.from_array([
        [2, -4],
        [3, 1],
        [-2, 1]
    ])
    mat2 = Matrix.from_array([
        [2, -2, 3],
        [-3, 4, -4]
    ])

    print(mat1 * mat2)