Thread: Help with Fast Matrix Exponentiation

hey everyone,

I feel like I am close to the answer, but I'm just missing something little. What I'm supposed to do, basically, is come up with a program that allows me to increase matrices exponentially. My problem lies when I want to do anything higher than a power of two. For example, when I raise it to the power of 3, it does it by 4 instead. If I do it by 4, it does it by 6. Can anyone help me? I feel like it's something small that I am overlooking, but I am not able to figure it out.

	import java.io.*;
	import java.util.Scanner;
	public class Matrix {
	  static int[][] mult(int[][] X, int[][] Y) {
	  int Z[][] = new int[2][2];
	  Z[0][0] = X[0][0]*Y[0][0] + X[0][1]*Y[1][0];
	  Z[0][1] = X[0][0]*Y[0][1] + X[0][1]*Y[1][1];
	  Z[1][0] = X[1][0]*Y[0][0] + X[1][1]*Y[0][1];
	  Z[1][1] = X[1][0]*Y[1][0] + X[1][1]*Y[1][1];
	  return Z;
	  }
	  public static void main(String argv[]) {
	    // create a scanner for interactive input
	    Scanner scin = new Scanner(System.in);
	    int matrix[][] = new int[2][2];
	    int B[][] = new int[2][2];
	    int A[][] = new int[2][2];
	    int k,n;
	    // Ask for the matrix
	    System.out.print("[ M[0][0] M[0][1] ] =  ");
	    matrix[0][0] = scin.nextInt(); matrix[0][1] = scin.nextInt();
	    System.out.print("[ M[1][0] M[1][1] ] =  ");
	    matrix[1][0] = scin.nextInt(); matrix[1][1] = scin.nextInt();
	    System.out.print("n =  ");
	    n = scin.nextInt();
	    k = n; B = matrix;
	    if ((k==1)) 
	    {
	    	A = matrix;
	    }
	    	else 
	    {
	    		int m=1;
	    		int C[][]=matrix;
	    		C[0][0]=1;C[0][1]=2;
	    		C[1][0]=3;C[1][1]=4;
	      while(m<n)
	      {
	    	  if(m==n)  
	    	  {
	    		  break;
	    	  }
	    	  m++;
 
	    	  A[0][0] = (C[0][0]*matrix[0][0])+(C[1][0]*matrix[0][1]); A[0][1] = (C[0][0]*matrix[0][1])+(C[0][1]*matrix[1][1]);
	    	  A[1][0] = (C[1][0]*matrix[0][0])+(C[1][1]*matrix[1][0]); A[1][1] = (C[1][0]*matrix[0][1])+(C[1][1]*matrix[1][1]);
 
	    	  C[0][0]=A[0][0];C[0][1]=A[0][1];
	    	  C[1][0]=A[1][0];C[1][1]=A[1][1];
 
 
 
	      }
	    }
	    while(k > 0) 
	    {
	      B= mult(B,B);
	      if ((k%1) == 1) A = mult(A,B);
	      k = k/2;
	}
	System.out.println( A[0][0] + "  " + A[0][1]);
	  System.out.println( A[1][0] + "  " + A[1][1]);
	}
	}

Ignore this, I found out what had happened from someone in my class about two hours later. Sorry for prematurely posting.