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aherbert pushed a commit to branch master
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commit 2286528976920008b523229608e6408101078648
Author: aherbert <aherb...@apache.org>
AuthorDate: Wed Aug 25 16:53:44 2021 +0100
Update observed frequencies with expected where appropriate.
The expected frequencies are obtained during the table construction.
They closely match the previously measured observed frequencies.
---
.../rng/sampling/distribution/ZigguratSampler.java | 45 +++++++++++-----------
1 file changed, 22 insertions(+), 23 deletions(-)
diff --git
a/commons-rng-sampling/src/main/java/org/apache/commons/rng/sampling/distribution/ZigguratSampler.java
b/commons-rng-sampling/src/main/java/org/apache/commons/rng/sampling/distribution/ZigguratSampler.java
index ad21c3f..564b274 100644
---
a/commons-rng-sampling/src/main/java/org/apache/commons/rng/sampling/distribution/ZigguratSampler.java
+++
b/commons-rng-sampling/src/main/java/org/apache/commons/rng/sampling/distribution/ZigguratSampler.java
@@ -563,15 +563,15 @@ public abstract class ZigguratSampler implements
SharedStateContinuousSampler {
if (i < I_MAX) {
// Early exit.
- // This branch is called about 0.984379 times per call into
createSample.
- // Note: Frequencies have been empirically measured for the
first call to
- // createSample; recursion due to retries have been ignored.
Frequencies sum to 1.
+ // Expected frequency = 0.984375
// Drop the sign bit to multiply by [0, 2^63).
return X[i] * (x & MAX_INT64);
}
- // For the first call into createSample:
- // Recursion frequency = 0.000515503
- // Overhang frequency = 0.0151056
+ // Expected frequency = 0.015625
+
+ // Tail frequency = 0.000516062 (recursion)
+ // Overhang frequency = 0.0151089
+
final int j = selectRegion();
// If the tail then exploit the memoryless property of the
exponential distribution.
// Add a new sample to the start of the tail (X_0).
@@ -622,17 +622,14 @@ public abstract class ZigguratSampler implements
SharedStateContinuousSampler {
// _FAST_PRNG_SAMPLE_X(xj, ux)
final double x = sampleX(X, j, u1);
if (uDistance >= E_MAX) {
- // Frequency (per call into createSample): 0.0126230
- // Frequency (per call into expOverhang): 0.823328
// Early Exit: x < y - epsilon
return x;
}
- // Frequency per call into createSample:
- // Return = 0.00248262
- // Recursion = 0.000226013
- // Frequency per call into expOverhang:
- // Return = 0.161930
- // Recursion = 0.0147417
+
+ // Note: Frequencies have been empirically measured per call into
expOverhang:
+ // Early Exit = 0.823328
+ // Accept Y = 0.161930
+ // Reject Y = 0.0147417 (recursion)
// _FAST_PRNG_SAMPLE_Y(j, pow(2, 63) - (ux + uDistance))
return sampleY(Y, j, u1 + uDistance) <= Math.exp(-x) ?
@@ -972,7 +969,7 @@ public abstract class ZigguratSampler implements
SharedStateContinuousSampler {
if (i < I_MAX) {
// Early exit.
- // Branch frequency: 0.988283
+ // Expected frequency = 0.988281
return X[i] * xx;
}
@@ -989,6 +986,8 @@ public abstract class ZigguratSampler implements
SharedStateContinuousSampler {
* @return a sample
*/
private double edgeSample(long xx) {
+ // Expected frequency = 0.0117188
+
// Recycle bits then advance RNG:
// u1 = RANDOM_INT63()
long u1 = xx & MAX_INT64;
@@ -1007,8 +1006,8 @@ public abstract class ZigguratSampler implements
SharedStateContinuousSampler {
double x;
if (j > J_INFLECTION) {
// Convex overhang
- // Branch frequency: 0.00892897
- // Loop repeat frequency: 0.389804
+ // Expected frequency: 0.00892899
+ // Observed loop repeat frequency: 0.389804
for (;;) {
x = sampleX(X, j, u1);
// u2 = u1 + (u2 - u1) = u1 + uDistance
@@ -1030,18 +1029,18 @@ public abstract class ZigguratSampler implements
SharedStateContinuousSampler {
} else if (j < J_INFLECTION) {
if (j == 0) {
// Tail
- // Branch frequency: 0.000276358
+ // Expected frequency: 0.000276902
// Note: Although less frequent than the next branch, j ==
0 is a subset of
// j < J_INFLECTION and must be first.
- // Loop repeat frequency: 0.0634786
+ // Observed loop repeat frequency: 0.0634786
do {
x = ONE_OVER_X_0 * exponential.sample();
} while (exponential.sample() < 0.5 * x * x);
x += X_0;
} else {
// Concave overhang
- // Branch frequency: 0.00249563
- // Loop repeat frequency: 0.0123784
+ // Expected frequency: 0.00249694
+ // Observed loop repeat frequency: 0.0123784
for (;;) {
// u2 = u1 + (u2 - u1) = u1 + uDistance
long uDistance = randomInt63() - u1;
@@ -1061,8 +1060,8 @@ public abstract class ZigguratSampler implements
SharedStateContinuousSampler {
}
} else {
// Inflection point
- // Branch frequency: 0.0000159359
- // Loop repeat frequency: 0.500213
+ // Expected frequency: 0.000015914
+ // Observed loop repeat frequency: 0.500213
for (;;) {
x = sampleX(X, j, u1);
if (sampleY(Y, j, randomInt63()) < Math.exp(-0.5 * x * x))
{
