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[apps/probability] Change geometric distribution definition

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THe distribution now represents the number of trials neded before a
success, so is defined for k in {1, 2, 3, ...}
This commit is contained in:
Léa Saviot
2020-05-11 16:27:37 +02:00
committed by Émilie Feral
parent d200688f20
commit a9c47a9468
2 changed files with 10 additions and 11 deletions
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17
apps/probability/distribution/geometric_distribution.cpp
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@@ -15,8 +15,7 @@ float GeometricDistribution::xMax() const {
}
float GeometricDistribution::yMax() const {
int maxAbscissa = 0;
float result = evaluateAtAbscissa(maxAbscissa);
float result = evaluateAtAbscissa(1.0); // Tha probability is max for x == 1
return result * (1.0f + k_displayTopMarginRatio);
}
@@ -29,16 +28,18 @@ bool GeometricDistribution::authorizedValueAtIndex(float x, int index) const {
}
template<typename T>
T GeometricDistribution::templatedApproximateAtAbscissa(T x) const {
if (x < 0) {
T GeometricDistribution::templatedApproximateAtAbscissa(T k) const {
constexpr T castedOne = static_cast<T>(1.0);
if (k < castedOne) {
return static_cast<T>(0.0);
}
T p = static_cast<T>(m_parameter1);
if (p == static_cast<T>(1.0)) {
return static_cast<T>(x == 0 ? 1.0 : 0.0);
if (p == castedOne) {
return k == castedOne ? castedOne : static_cast<T>(0.0);
}
T lResult = x * std::log(static_cast<T>(1.0) - p);
return p*std::exp(lResult);
// The result is p * (1-p)^{k-1}
T lResult = (k - castedOne) * std::log(castedOne - p);
return p * std::exp(lResult);
}
}

4
apps/probability/distribution/geometric_distribution.h
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@@ -7,9 +7,7 @@ namespace Probability {
/* We chose the definition:
* 0 < p <= 1 for success probability
* k failures where k ∈ {0, 1, 2, ... }
* The distribution follows the probability distribution of the number of failures before
* the first success. */
* k number of trials needed to get one success, where k ∈ {1, 2, 3, ...}. */
class GeometricDistribution final : public OneParameterDistribution {
public: