[apps/proba] Implement Fisher formulae

apps/probability/distribution/fisher_distribution.cpp

@@ -1,10 +1,13 @@
 #include "fisher_distribution.h"
-#include <poincare/normal_distribution.h>
+#include <poincare/beta_function.h>
+#include <poincare/regularized_incomplete_beta_function.h>
 #include <cmath>
 #include <float.h>
 
 namespace Probability {
 
+static inline double maxDouble(double x, double y) { return x > y ? x : y; }
+
 float FisherDistribution::xMin() const {
   return -k_displayLeftMarginRatio * xMax();
 }
@@ -39,7 +42,15 @@ I18n::Message FisherDistribution::parameterDefinitionAtIndex(int index) {
 }
 
 float FisherDistribution::evaluateAtAbscissa(float x) const {
-  return 1.0; //TODO LEA Poincare::FisherDistribution::EvaluateAtAbscissa(x, m_parameter1, m_parameter2);
+  if (x < 0.0f) {
+    return NAN;
+  }
+  const float d1 = m_parameter1;
+  const float d2 = m_parameter2;
+  const float f = d1*x/(d1*x+d2);
+  const float numerator = std::pow(f, d1/2.0f) * std::pow(1.0f - f, d2/2.0f);
+  const float denominator = x * Poincare::BetaFunction(d1/2.0f, d2/2.0f);
+  return numerator / denominator;
 }
 
 bool FisherDistribution::authorizedValueAtIndex(float x, int index) const {
@@ -53,11 +64,22 @@ void FisherDistribution::setParameterAtIndex(float f, int index) {
 }
 
 double FisherDistribution::cumulativeDistributiveFunctionAtAbscissa(double x) const {
-  return 1.0; //TODO LEA
+  const double d1 = m_parameter1;
+  const double d2 = m_parameter2;
+  return Poincare::RegularizedIncompleteBetaFunction(d1/2.0, d2/2.0, d1*x/(d1*x+d2));
 }
 
 double FisherDistribution::cumulativeDistributiveInverseForProbability(double * probability) {
-  return 1.0; //TODO LEA
+  /* We have to compute the values of the interval in which to look for x.
+   * We cannot put xMin because xMin is < 0 for display purposes, and negative
+   * values are not accepted.
+   * The maximum of the interval: we want */
+  if (*probability < DBL_EPSILON) {
+    return 0.0;
+  }
+  return cumulativeDistributiveInverseForProbabilityUsingIncreasingFunctionRoot(probability, DBL_EPSILON, maxDouble(xMax(), 100.0));  // Ad-hoc value;
+
+
 }
 
 }

poincare/Makefile

@@ -30,6 +30,7 @@ poincare_src += $(addprefix poincare/src/,\
 
 poincare_src += $(addprefix poincare/src/,\
   init.cpp \
+  beta_function.cpp \
   binomial_distribution.cpp \
   erf_inv.cpp \
   exception_checkpoint.cpp \

poincare/include/poincare/beta_function.h

@@ -0,0 +1,37 @@
+#ifndef POINCARE_BETA_FUNCTION_H
+#define POINCARE_BETA_FUNCTION_H
+
+/*
+ * zlib License
+ *
+ * Regularized Incomplete Beta Function
+ *
+ * Copyright (c) 2016, 2017 Lewis Van Winkle
+ * http://CodePlea.com
+ *
+ * This software is provided 'as-is', without any express or implied
+ * warranty. In no event will the authors be held liable for any damages
+ * arising from the use of this software.
+ *
+ * Permission is granted to anyone to use this software for any purpose,
+ * including commercial applications, and to alter it and redistribute it
+ * freely, subject to the following restrictions:
+ *
+ * 1. The origin of this software must not be misrepresented; you must not
+ *    claim that you wrote the original software. If you use this software
+ *    in a product, an acknowledgement in the product documentation would be
+ *    appreciated but is not required.
+ * 2. Altered source versions must be plainly marked as such, and must not be
+ *    misrepresented as being the original software.
+ * 3. This notice may not be removed or altered from any source distribution.
+ */
+
+
+// WARNING: this code has been modified
+namespace Poincare {
+
+double BetaFunction(double a, double b);
+
+}
+
+#endif

poincare/src/beta_function.cpp

@@ -0,0 +1,14 @@
+#include <poincare/beta_function.h>
+#include <math.h>
+#include <cmath>
+
+namespace Poincare {
+
+double BetaFunction(double a, double b) {
+  if (a < 0.0 || b < 0.0) {
+    return NAN;
+  }
+  return std::exp(std::lgamma(a) + std::lgamma(b) - std::lgamma(a+b));
+}
+
+}