Examples of com.facebook.LinkBench.distributions.ProbabilityDistribution

Package com.facebook.LinkBench.distributions

Examples of com.facebook.LinkBench.distributions.ProbabilityDistribution

com.facebook.LinkBench.distributions.ProbabilityDistribution
Probability distribution over a range of integers [min, max), ranked in descending order of probability, where min is most probable and max - 1 is least probable. @author tarmstrong

  /**
   * Check a few invariants cdf should adhere to
   */
  @Test
  public void testCDFSanity() {
    ProbabilityDistribution dist = getDist();
    long min = 453, max = 26546454;
    dist.init(min, max, getDistParams(), "");


    assertEquals(dist.cdf(min-1), 0.0);
    assertEquals(dist.cdf(min-234321), 0.0);
    assertEquals(dist.cdf(max), 1.0);
    assertEquals(dist.cdf(max+2343242224234L), 1.0);


    // Check cdf is monotonically increasing
    double last = 0.0;
    long step = (max - min) / cdfChecks();
    for (long id = min; id < max; id += step) {
      double p = dist.cdf(id);
      assertTrue(p >= last);
      last = p;
    }
  }

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    }
  }


  @Test
  public void testPDFSanity() {
    ProbabilityDistribution dist = getDist();
    long min = 453, max = 26546454;
    dist.init(min, max, getDistParams(), "");


    assertEquals(0.0, dist.pdf(min-1));
    assertEquals(0.0, dist.pdf(min-234321));
    assertEquals(0.0, dist.pdf(max));
    assertEquals(0.0, dist.pdf(max+2343242224234L));


    // Check pdf is in correct range
    double total = 0.0;
    long step = (max - min) / pdfChecks();
    for (long id = min; id < max; id += step) {
      double p = dist.pdf(id);
      if ((id - min) < step * 100) {
        System.err.println("p(X=" + id + ") = " + p);
      }
      assertTrue(p >= 0.0);
      assertTrue(p <= 1.0);

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    assert(total <= 1.0);
  }


  @Test
  public void testPDFSum() {
    ProbabilityDistribution dist = getDist();
    long min = 1, max = 50;
    dist.init(min, max, getDistParams(), "");


    // Check sum of pdf over small range
    // Order of least to most probably to minimize sum error
    double total = 0.0;
    for (long id = max - 1; id >= min; id--) {
      double p = dist.pdf(id);
      assertTrue(p >= 0.0);
      assertTrue(p <= 1.0);
      System.err.println("p(X=" + id + ") = " + p);
      total += p;
    }

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    assertTrue(total >= 0.95 );
  }


  @Test
  public void testChooseSanity() {
    ProbabilityDistribution dist = getDist();
    long min = 453, max = 26546454;
    dist.init(min, max, getDistParams(), "");
    Random rng = initRandom("testChooseSanity");
    for (int i = 0; i < 100000; i++) {
      long id = dist.choose(rng);
      assertTrue(id >= min);
      assertTrue(id < max);
    }
  }

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    int buckets[] = new int[bucketCount];


    long n = max - min;


    Random rng = initRandom("testCDFChooseConsistency");
    ProbabilityDistribution dist = getDist();
    dist.init(min, max, getDistParams(), "");


    int trials = 1000000;
    for (int i = 0; i < trials; i++) {
      long id = dist.choose(rng);
      long off = id - min;
      int bucket = bucketer.chooseBucket(off, n);
      buckets[bucket]++;
    }


    int totalCount = 0;
    boolean fail = false;
    for (int b = 0; b < bucketCount; b++) {
      totalCount += buckets[b];
      long bucketTop = bucketer.bucketMax(b, n) + min;
      double actCDF = ((double)totalCount) / trials;
      double expCDF = dist.cdf(bucketTop);
      // 0.2% error
      if (Math.abs(expCDF - actCDF) > tolerance()) {
        System.err.println(String.format("Divergence between CDF and " +
            "choose function: P(X <= %d) act: %f exp: %f", bucketTop,
            actCDF, expCDF));

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  }


  @Test
  public void testCDFPDFConsistency() {
    long min = 252352, max = 6544543;
    ProbabilityDistribution dist = getDist();
    dist.init(min, max, getDistParams(), "");


    long step = (max - min) / cdfChecks();
    for (long id = min + 1; id < max; id += step) {
      double c = dist.cdf(id);
      double c1 = dist.cdf(id - 1);
      double p = dist.pdf(id);


      double err = Math.abs((c - c1) - p);
      if (err > 0.0001) {
        fail(String.format("Error > 0.001: cdf(%d) - cdf(%d) = %f, pdf(%d) = %f",
                              id, id -1, c1 - c, id, p));

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  }


  @Test
  public void testQuantileSanity() {
    long min = 0, max = 1000;
    ProbabilityDistribution dist = getDist();
    dist.init(min, max, getDistParams(), "");


    long last = dist.quantile(0.0);
    for (double q = 0.0; q <= 1.0; q += 0.125) {
      long id = dist.quantile(q);
      System.err.format("quantile(%f) = %d\n", q, id);
      assertTrue(id >= min);
      assertTrue(id < max);
      assertTrue(id >= last);
      last = id;
    }


    // min should be most probable, and therefore should definitely
    // be returned by quantile
    assertEquals(min, dist.quantile(0.0));
  }

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Related Classes of com.facebook.LinkBench.distributions.ProbabilityDistribution

com.facebook.LinkBench.DistributionTestBase

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