Illustration of matrix transposition time performance effects due to cache configuration

MatrixTranspose.java

class MatrixTranspose {  
  public static void matrixTranspose(){
    	long startTime, elapsedTime;
    	int n = 10000;
    	int a[][] = new int[n][n];
    	int b[][] = new int[n][n];
    	
    	// #######################################
    	for (int i = 0; i < n; i++){
    		for (int j = 0; j < n; j++){
    			a[i][j] = (int) (100 * Math.random());
    			b[i][j] = (int) (100 * Math.random());
    		}
    	}
    	System.out.print("Version 1 (iterative): ");
    	startTime = System.currentTimeMillis();
    	for (int i = 0; i < n; i++){
    		for (int j = 0; j < n; j++){
    			b[i][j] = a[j][i];
    		}
    	}
    	elapsedTime = System.currentTimeMillis() - startTime;
    	System.out.println("Elapsed time: " + elapsedTime + "ms.");
    	
    	// #######################################
    	for (int i = 0; i < n; i++){
    		for (int j = 0; j < n; j++){
    			a[i][j] = (int) (100 * Math.random());
    			b[i][j] = (int) (100 * Math.random());
    		}
    	}
    	System.out.print("Version 2 (iterative by block - K=10): ");
    	int K = 10;
    	startTime = System.currentTimeMillis();
    	for (int I = 0; I < n; I += K){
    		for (int J = 0; J < n; J += K){
    			for (int i = K; i < Math.min(I + K, n); i++){
    				for (int j = K; j < Math.min(J + K, n); j++){
    					b[i][j] = a[j][i];
    				}
    			}
    		}
    	}
    	elapsedTime = System.currentTimeMillis() - startTime;
    	System.out.println("Elapsed time: " + elapsedTime + "ms.");
    }
    
    public static void main(String args[]){
        matrixTanspose();
    }
}