dist.h

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#pragma once
 
#include <cmath>
 
#include "config.h"
#include "util/points.h"
 
namespace alfi::dist {
    enum class Type {
        GENERAL,
        UNIFORM,
        QUADRATIC,
        CUBIC,
        CHEBYSHEV,
        CHEBYSHEV_STRETCHED,
        CHEBYSHEV_ELLIPSE,
        CHEBYSHEV_ELLIPSE_STRETCHED,
        CIRCLE_PROJECTION,
        ELLIPSE_PROJECTION,
        LOGISTIC,
        LOGISTIC_STRETCHED,
        ERF,
        ERF_STRETCHED,
    };
 
    template <typename Number = DefaultNumber, template <typename, typename...> class Container = DefaultContainer>
    Container<Number> uniform(SizeT n, Number a, Number b) {
        if (n == 1)
            return {(a+b)/2};
        Container<Number> points(n);
        for (SizeT i = 0; i < n; ++i) {
            points[i] = a + (b - a) * static_cast<Number>(i) / static_cast<Number>(n - 1);
        }
        return points;
    }

    template <typename Number = DefaultNumber, template <typename, typename...> class Container = DefaultContainer>
    Container<Number> quadratic(SizeT n, Number a, Number b) {
        if (n == 1)
            return {(a+b)/2};
        Container<Number> points(n);
        for (SizeT i = 0; i < n; ++i) {
            const Number x = 2 * static_cast<Number>(i) / (static_cast<Number>(n) - 1) - 1;
            const Number value = x <= 0 ? x * (x + 2) : -x * (x - 2);
            points[i] = a + (b - a) * (1 + value) / 2;
        }
        return points;
    }

    template <typename Number = DefaultNumber, template <typename, typename...> class Container = DefaultContainer>
    Container<Number> cubic(SizeT n, Number a, Number b) {
        if (n == 1)
            return {(a+b)/2};
        Container<Number> points(n);
        for (SizeT i = 0; i < n; ++i) {
            const Number x = 2 * static_cast<Number>(i) / (static_cast<Number>(n) - 1) - 1;
            const Number value = (3 - x*x) * x / 2;
            points[i] = a + (b - a) * (1 + value) / 2;
        }
        return points;
    }
 
    template <typename Number = DefaultNumber, template <typename, typename...> class Container = DefaultContainer>
    Container<Number> chebyshev(SizeT n, Number a, Number b) {
        if (n == 1)
            return {(a+b)/2};
        Container<Number> points(n);
        for (SizeT i = 0; i < n; ++i) {
            const Number x = std::cos(M_PI * (2 * (static_cast<Number>(n) - static_cast<Number>(i)) - 1) / (2 * static_cast<Number>(n)));
            points[i] = a + (x + 1) * (b - a) / 2;
        }
        return points;
    }
 
    template <typename Number = DefaultNumber, template <typename, typename...> class Container = DefaultContainer>
    Container<Number> chebyshev_stretched(SizeT n, Number a, Number b) {
        return points::stretched<Number,Container>(chebyshev(n, a, b), a, b);
    }
 
    template <typename Number = DefaultNumber, template <typename, typename...> class Container = DefaultContainer>
    Container<Number> chebyshev_ellipse(SizeT n, Number a, Number b, Number ratio) {
        Container<Number> points(n);
        for (SizeT i = 0; i < n / 2; ++i) {
            const Number theta = M_PI * (2 * static_cast<Number>(i) + 1) / (2 * static_cast<Number>(n));
            const Number x = 1 / std::sqrt(1 + std::pow(std::tan(theta) / ratio, 2));
            points[i] = a + (1 - x) * (b - a) / 2;
            points[n-1-i] = a + (1 + x) * (b - a) / 2;
        }
        if (n % 2 == 1)
            points[n/2] = (a+b)/2;
        return points;
    }
 
    template <typename Number = DefaultNumber, template <typename, typename...> class Container = DefaultContainer>
    Container<Number> chebyshev_ellipse_stretched(SizeT n, Number a, Number b, Number ratio) {
        return points::stretched<Number,Container>(chebyshev_ellipse(n, a, b, ratio), a, b);
    }
 
    template <typename Number = DefaultNumber, template <typename, typename...> class Container = DefaultContainer>
    Container<Number> circle_proj(SizeT n, Number a, Number b) {
        if (n == 1)
            return {(a+b)/2};
        Container<Number> points(n);
        for (SizeT i = 0; i < n; ++i) {
            const Number x = 1 - std::cos(M_PI * static_cast<Number>(i) / (static_cast<Number>(n) - 1));
            points[i] = a + (b - a) * x / 2;
        }
        return points;
    }
 
    template <typename Number = DefaultNumber, template <typename, typename...> class Container = DefaultContainer>
    Container<Number> ellipse_proj(SizeT n, Number a, Number b, Number ratio) {
        Container<Number> points(n);
        for (SizeT i = 0; i < n / 2; ++i) {
            const Number theta = M_PI * static_cast<Number>(i) / (static_cast<Number>(n) - 1);
            const Number x = 1 / std::sqrt(1 + std::pow(std::tan(theta) / ratio, 2));
            points[i] = (1 - x) * (b - a) / 2 + a;
            points[n-1-i] = (1 + x) * (b - a) / 2 + a;
        }
        if (n % 2 == 1)
            points[n/2] = (a+b)/2;
        return points;
    }

    template <typename Number = DefaultNumber, template <typename, typename...> class Container = DefaultContainer>
    Container<Number> logistic(SizeT n, Number a, Number b, Number steepness) {
        if (n == 1)
            return {(a+b)/2};
        Container<Number> points(n);
        for (SizeT i = 0; i < n; ++i) {
            const Number x = 2 * static_cast<Number>(i) / (static_cast<Number>(n) - 1) - 1;
            const Number logisticValue = 1 / (1 + std::exp(-steepness * x));
            points[i] = a + (b - a) * logisticValue;
        }
        return points;
    }
 
    template <typename Number = DefaultNumber, template <typename, typename...> class Container = DefaultContainer>
    Container<Number> logistic_stretched(SizeT n, Number a, Number b, Number steepness) {
        if (n == 0)
            return {};
        if (n == 1)
            return {(a+b)/2};
        Container<Number> points(n);
        const Number stretch_factor = 1 - 2 / (1 + std::exp(steepness));
        for (SizeT i = 1; i < n - 1; ++i) {
            const Number x = 2 * static_cast<double>(i) / (static_cast<Number>(n) - 1) - 1;
            const Number logisticValue = 1 / (1 + std::exp(-steepness * x));
            const Number stretched = (logisticValue - 1 / (1 + std::exp(steepness))) / stretch_factor;
            points[i] = a + (b - a) * stretched;
        }
        points[0] = a;
        points[n-1] = b;
        return points;
    }

    template <typename Number = DefaultNumber, template <typename, typename...> class Container = DefaultContainer>
    Container<Number> erf(SizeT n, Number a, Number b, Number steepness) {
        if (n == 0)
            return {};
        if (n == 1)
            return {(a+b)/2};
        Container<Number> points(n);
        for (SizeT i = 0; i < n; ++i) {
            const Number x = 2 * static_cast<Number>(i) / (static_cast<Number>(n) - 1) - 1;
            const Number erf_value = std::erf(steepness * x);
            points[i] = a + (b - a) * (1 + erf_value) / 2;
        }
        return points;
    }
 
    template <typename Number = DefaultNumber, template <typename, typename...> class Container = DefaultContainer>
    Container<Number> erf_stretched(SizeT n, Number a, Number b, Number steepness) {
        return points::stretched<Number,Container>(erf(n, a, b, steepness), a, b);
    }
 
    template <typename Number = DefaultNumber, template <typename, typename...> class Container = DefaultContainer>
    Container<Number> of_type(Type type, SizeT n, Number a, Number b, Number parameter = NAN) {
        switch (type) {
        case Type::QUADRATIC:
            return quadratic(n, a, b);
        case Type::CUBIC:
            return cubic(n, a, b);
        case Type::CHEBYSHEV:
            return chebyshev(n, a, b);
        case Type::CHEBYSHEV_STRETCHED:
            return chebyshev_stretched(n, a, b);
        case Type::CHEBYSHEV_ELLIPSE:
            return chebyshev_ellipse(n, a, b, parameter);
        case Type::CHEBYSHEV_ELLIPSE_STRETCHED:
            return chebyshev_ellipse_stretched(n, a, b, parameter);
        case Type::CIRCLE_PROJECTION:
            return circle_proj(n, a, b);
        case Type::ELLIPSE_PROJECTION:
            return ellipse_proj(n, a, b, parameter);
        case Type::LOGISTIC:
            return logistic(n, a, b, parameter);
        case Type::LOGISTIC_STRETCHED:
            return logistic_stretched(n, a, b, parameter);
        case Type::ERF:
            return erf(n, a, b, parameter);
        case Type::ERF_STRETCHED:
            return erf_stretched(n, a, b, parameter);
        case Type::UNIFORM:
        case Type::GENERAL:
        default:
            return uniform(n, a, b);
        }
    }
}