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The Apache Commons Codec package contains simple encoder and decoders for
various formats such as Base64 and Hexadecimal. In addition to these
widely used encoders and decoders, the codec package also maintains a
collection of phonetic encoding utilities.
/* ====================================================================
Licensed to the Apache Software Foundation (ASF) under one or more
contributor license agreements. See the NOTICE file distributed with
this work for additional information regarding copyright ownership.
The ASF licenses this file to You under the Apache License, Version 2.0
(the "License"); you may not use this file except in compliance with
the License. You may obtain a copy of the License at
http://www.apache.org/licenses/LICENSE-2.0
Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
==================================================================== */
package org.apache.poi.ss.formula.functions;
import org.apache.poi.ss.formula.eval.BoolEval;
import org.apache.poi.ss.formula.eval.ErrorEval;
import org.apache.poi.ss.formula.eval.EvaluationException;
import org.apache.poi.ss.formula.eval.NumberEval;
import org.apache.poi.ss.formula.eval.ValueEval;
public class Poisson {
private static final double DEFAULT_RETURN_RESULT =1;
/** All long-representable factorials */
private static final long[] FACTORIALS = {
1L, 1L, 2L,
6L, 24L, 120L,
720L, 5040L, 40320L,
362880L, 3628800L, 39916800L,
479001600L, 6227020800L, 87178291200L,
1307674368000L, 20922789888000L, 355687428096000L,
6402373705728000L, 121645100408832000L, 2432902008176640000L };
/**
* This checks is x = 0 and the mean = 0.
* Excel currently returns the value 1 where as the
* maths common implementation will error.
* @param x The number.
* @param mean The mean.
* @return If a default value should be returned.
*/
private static boolean isDefaultResult(double x, double mean) {
return x == 0 && mean == 0;
}
private static void checkArgument(double aDouble) throws EvaluationException {
NumericFunction.checkValue(aDouble);
// make sure that the number is positive
if (aDouble < 0) {
throw new EvaluationException(ErrorEval.NUM_ERROR);
}
}
private static double probability(int k, double lambda) {
return Math.pow(lambda, k) * Math.exp(-lambda) / factorial(k);
}
private static double cumulativeProbability(int x, double lambda) {
double result = 0;
for(int k = 0; k <= x; k++){
result += probability(k, lambda);
}
return result;
}
private static long factorial(final int n) {
if (n < 0 || n > 20) {
throw new IllegalArgumentException("Valid argument should be in the range [0..20]");
}
return FACTORIALS[n];
}
public static ValueEval evaluate(ValueEval[] args, int srcRowIndex, int srcColumnIndex) {
if (args.length != 3) {
return ErrorEval.VALUE_INVALID;
}
ValueEval arg0 = args[0];
ValueEval arg1 = args[1];
ValueEval arg2 = args[2];
try {
// arguments/result for this function
double x = NumericFunction.singleOperandEvaluate(arg0, srcRowIndex, srcColumnIndex);
double mean = NumericFunction.singleOperandEvaluate(arg1, srcRowIndex, srcColumnIndex);
// check for default result : excel implementation for 0,0
// is different to Math Common.
if (isDefaultResult(x,mean)) {
return new NumberEval(DEFAULT_RETURN_RESULT);
}
// check the arguments : as per excel function def
checkArgument(x);
checkArgument(mean);
// truncate x : as per excel function def
boolean cumulative = ((BoolEval)arg2).getBooleanValue();
double result = cumulative ? cumulativeProbability((int) x, mean) : probability((int) x, mean);
// check the result
NumericFunction.checkValue(result);
return new NumberEval(result);
} catch (EvaluationException e) {
return e.getErrorEval();
}
}
}