logistic_model.cpp
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#include "logistic_model.h"
#include <math.h>
#include <assert.h>
#include "../../poincare/include/poincare_layouts.h"
using namespace Poincare;
namespace Regression {
ExpressionLayout * LogisticModel::layout() {
static ExpressionLayout * layout = nullptr;
if (layout == nullptr) {
const ExpressionLayout * exponentLayoutChildren[] = {
new CharLayout('-', KDText::FontSize::Small),
new CharLayout('b', KDText::FontSize::Small),
new CharLayout(Ion::Charset::MiddleDot, KDText::FontSize::Small),
new CharLayout('X', KDText::FontSize::Small)
};
const ExpressionLayout * layoutChildren[] = {
new CharLayout('1', KDText::FontSize::Small),
new CharLayout('+', KDText::FontSize::Small),
new CharLayout('a', KDText::FontSize::Small),
new CharLayout(Ion::Charset::MiddleDot, KDText::FontSize::Small),
new CharLayout('e', KDText::FontSize::Small),
new VerticalOffsetLayout(
new HorizontalLayout(exponentLayoutChildren, 4, false),
VerticalOffsetLayout::Type::Superscript,
false)
};
layout = new FractionLayout(
new CharLayout('c', KDText::FontSize::Small),
new HorizontalLayout(layoutChildren, 6, false),
false);
}
return layout;
}
double LogisticModel::evaluate(double * modelCoefficients, double x) const {
double a = modelCoefficients[0];
double b = modelCoefficients[1];
double c = modelCoefficients[2];
return c/(1.0+a*exp(-b*x));
}
double LogisticModel::levelSet(double * modelCoefficients, double xMin, double step, double xMax, double y, Poincare::Context * context) {
double a = modelCoefficients[0];
double b = modelCoefficients[1];
double c = modelCoefficients[2];
if (a == 0 || b == 0 || c == 0 || y == 0) {
return NAN;
}
double lnArgument = (c/y - 1)/a;
if (lnArgument <= 0) {
return NAN;
}
return -log(lnArgument)/b;
}
double LogisticModel::partialDerivate(double * modelCoefficients, int derivateCoefficientIndex, double x) const {
double a = modelCoefficients[0];
double b = modelCoefficients[1];
double c = modelCoefficients[2];
double denominator = 1.0+a*exp(-b*x);
if (derivateCoefficientIndex == 0) {
// Derivate: exp(-b*x)*(-1 * c/(1.0+a*exp(-b*x))^2)
return -exp(-b*x) * c/(denominator * denominator);
}
if (derivateCoefficientIndex == 1) {
// Derivate: (-x)*a*exp(-b*x)*(-1/(1.0+a*exp(-b*x))^2)
return x*a*exp(-b*x)*c/(denominator * denominator);
}
if (derivateCoefficientIndex == 2) {
// Derivate: (-x)*a*exp(-b*x)*(-1/(1.0+a*exp(-b*x))^2)
return 1.0/denominator;
}
assert(false);
return 0.0;
}
}