ConstantCurve.h

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#ifndef COOLPROP_REGION_CONSTANT_CURVE_H
#define COOLPROP_REGION_CONSTANT_CURVE_H
 
#include <stdexcept>
 
#include "CoolProp/region/BoundaryCurve.h"
 
namespace CoolProp {
namespace region {
 
// Trivial BoundaryCurve b(a) = c, used for fixed ceilings/floors such as
// a T_max or p_max plane.  All three queries are O(1).
class ConstantCurve final : public BoundaryCurve
{
   public:
    ConstantCurve(double a_lo, double a_hi, double b_value) : a_lo_(a_lo), a_hi_(a_hi), b_(b_value) {
        if (!(a_hi_ > a_lo_)) {
            throw std::invalid_argument("ConstantCurve: a_hi must exceed a_lo");
        }
    }
 
    // Plain-data snapshot for serialization.  Safe to expose because
    // the only invariant ConstantCurve enforces (a_hi > a_lo) is
    // re-checked by the constructor.
    struct State
    {
        double a_lo;
        double a_hi;
        double b;
    };
    [[nodiscard]] State state() const noexcept {
        return State{a_lo_, a_hi_, b_};
    }
 
    [[nodiscard]] double eval(double /*a*/) const noexcept override {
        return b_;
    }
 
    // db/da is exactly zero — analytic derivative of the constant function.
    [[nodiscard]] double eval_da(double /*a*/) const noexcept override {
        return 0.0;
    }
 
    [[nodiscard]] std::pair<double, double> bounds() const noexcept override {
        return {b_, b_};
    }
 
    [[nodiscard]] std::pair<double, double> a_range() const noexcept override {
        return {a_lo_, a_hi_};
    }
 
   private:
    double a_lo_;
    double a_hi_;
    double b_;
};
 
}  // namespace region
}  // namespace CoolProp
 
#endif  // COOLPROP_REGION_CONSTANT_CURVE_H