/****************************************************************************** * Compilation: javac RandomSurferHistogram.java * Execution: java RandomSurferHistogram T * Data files: https://introcs.cs.princeton.edu/java/16pagerank/tinyG.txt * https://introcs.cs.princeton.edu/java/16pagerank/mediumG.txt * * % java Transition < tinyG.txt | java RandomSurferHistogram 1000000 * 0.27297 0.26583 0.14598 0.24729 0.06793 * ******************************************************************************/ public class RandomSurferHistogram { public static void main(String[] args) { StdDraw.enableDoubleBuffering(); int trials = Integer.parseInt(args[0]); // number of moves int n = StdIn.readInt(); // number of pages StdIn.readInt(); // ignore integer required by input format // Read transition matrix. double[][] p = new double[n][n]; // p[i][j] = prob. that surfer moves from page i to page j for (int i = 0; i < n; i++) for (int j = 0; j < n; j++) p[i][j] = StdIn.readDouble(); int[] freq = new int[n]; // freq[i] = # times surfer hits page i // Start at page 0. int page = 0; for (int t = 0; t < trials; t++) { // Make one random move. double r = Math.random(); double sum = 0.0; for (int j = 0; j < n; j++) { // Find interval containing r. sum += p[page][j]; if (r < sum) { page = j; break; } } freq[page]++; // plot histogram of frequencies StdDraw.clear(); StdDraw.setXscale(-1, n); StdDraw.setYscale(0, trials); for (int k = 0; k < n; k++) { StdDraw.filledRectangle(k, freq[k]/2.0, 0.25, freq[k]/2.0); } StdDraw.show(); StdDraw.pause(20); } // Print page ranks. for (int i = 0; i < n; i++) { StdOut.printf("%8.5f", (double) freq[i] / trials); } StdOut.println(); } }