Remove PoissonDistribution normalApproximateProbability
diff --git a/commons-statistics-distribution/src/main/java/org/apache/commons/statistics/distribution/PoissonDistribution.java b/commons-statistics-distribution/src/main/java/org/apache/commons/statistics/distribution/PoissonDistribution.java
index bfcabed..7cfe1d0 100644
--- a/commons-statistics-distribution/src/main/java/org/apache/commons/statistics/distribution/PoissonDistribution.java
+++ b/commons-statistics-distribution/src/main/java/org/apache/commons/statistics/distribution/PoissonDistribution.java
@@ -30,8 +30,6 @@
private static final int DEFAULT_MAX_ITERATIONS = 10000000;
/** Default convergence criterion. */
private static final double DEFAULT_EPSILON = 1e-12;
- /** Distribution used to compute normal approximation. */
- private final NormalDistribution normal;
/** Mean of the distribution. */
private final double mean;
/** Maximum number of iterations for cumulative probability. */
@@ -68,8 +66,6 @@
mean = p;
this.epsilon = epsilon;
this.maxIterations = maxIterations;
-
- normal = new NormalDistribution(p, Math.sqrt(p));
}
/** {@inheritDoc} */
@@ -117,22 +113,6 @@
maxIterations);
}
- /**
- * Calculates the Poisson distribution function using a normal
- * approximation. The {@code N(mean, sqrt(mean))} distribution is used
- * to approximate the Poisson distribution. The computation uses
- * "half-correction" (evaluating the normal distribution function at
- * {@code x + 0.5}).
- *
- * @param x Upper bound, inclusive.
- * @return the distribution function value calculated using a normal
- * approximation.
- */
- public double normalApproximateProbability(int x) {
- // Calculate the probability using half-correction.
- return normal.cumulativeProbability(x + 0.5);
- }
-
/** {@inheritDoc} */
@Override
public double getMean() {
diff --git a/commons-statistics-distribution/src/test/java/org/apache/commons/statistics/distribution/PoissonDistributionTest.java b/commons-statistics-distribution/src/test/java/org/apache/commons/statistics/distribution/PoissonDistributionTest.java
index dd95696..7257887 100644
--- a/commons-statistics-distribution/src/test/java/org/apache/commons/statistics/distribution/PoissonDistributionTest.java
+++ b/commons-statistics-distribution/src/test/java/org/apache/commons/statistics/distribution/PoissonDistributionTest.java
@@ -109,24 +109,6 @@
//-------------------- Additional test cases -------------------------------
/**
- * Test the normal approximation of the Poisson distribution by
- * calculating P(90 ≤ X ≤ 110) for X = Po(100) and
- * P(9900 ≤ X ≤ 10200) for X = Po(10000)
- */
- @Test
- void testNormalApproximateProbability() {
- PoissonDistribution dist = new PoissonDistribution(100);
- double result = dist.normalApproximateProbability(110) -
- dist.normalApproximateProbability(89);
- Assertions.assertEquals(0.706281887248, result, 1e-10);
-
- dist = new PoissonDistribution(10000);
- result = dist.normalApproximateProbability(10200) -
- dist.normalApproximateProbability(9899);
- Assertions.assertEquals(0.820070051552, result, 1E-10);
- }
-
- /**
* Test the degenerate cases of a 0.0 and 1.0 inverse cumulative probability.
*/
@Test
