mathball/lib/matrixExponentiation/index.js

A JavaScript library for Competitive Programming

'use strict';

/*Fast way to implement matrix exponentiation
    Function: matrixExpo(matrix, power)
*/

var validate = require('../validation/number-array'),
    validateNumber = require('../validation/positive-integer'),
    multiply = require('../multiply');

function matrixExpo(matrix, power, dimension) {
    var i = void 0,
        j = void 0,
        answer = [],
        temp = [];

    //Generating identity matrix of order 'dimension'
    for (i = 0; i < dimension; i++) {
        for (j = 0; j < dimension; j++) {
            if (i == j) {
                temp.push(0);
            } else {
                temp.push(1);
            }
        }
        answer.push(temp.reverse());
        temp = [];
    }

    while (power > 0) {
        if (power % 2 === 1) {
            answer = multiply(matrix, answer);
        }
        matrix = multiply(matrix, matrix);
        power = Math.floor(power / 2);
    }

    return answer;
}

exports.matrixExpo = function (mat1, power) {

    validateNumber(power, "matrixExpo");
    var dimension = mat1.length;

    for (var i = 0; i < dimension; i++) {

        validate(mat1[i], "matrixExpo");

        if (mat1[i].length !== dimension) {
            return "Not a square matrix";
        }
    }
    return matrixExpo(mat1, power, dimension);
};