Spline.cpp

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#include "Spline.h"
#include "MatrixMath.h"
#include "CPExceptions.h"
#include "CoolPropTools.h"

SplineClass::SplineClass()
{
        Nconstraints = 0;
        A.resize(4, std::vector<double>(4, 0));
        B.resize(4,0);
}
bool SplineClass::build()
{
        if (Nconstraints == 4)
        {
                std::vector<double> abcd = linsolve(A,B);
                a = abcd[0];
                b = abcd[1];
                c = abcd[2];
                d = abcd[3];
        return true;
        }
        else
        {
                throw ValueError(format("Number of constraints[%d] is not equal to 4",Nconstraints));
        }
}
bool SplineClass::add_value_constraint(double x, double y)
{
        int i = Nconstraints;
        if (i == 4)
                return false;
        A[i][0] = x*x*x;
        A[i][1] = x*x;
        A[i][2] = x;
        A[i][3] = 1;
        B[i] = y;
        Nconstraints++;
        return true;
}
void SplineClass::add_4value_constraints(double x1, double x2, double x3, double x4, double y1, double y2, double y3, double y4)
{
        add_value_constraint(x1, y1);
        add_value_constraint(x2, y2);
        add_value_constraint(x3, y3);
        add_value_constraint(x4, y4);
}
bool SplineClass::add_derivative_constraint(double x, double dydx)
{
        int i = Nconstraints;
        if (i == 4)
                return false;
        A[i][0] = 3*x*x;
        A[i][1] = 2*x;
        A[i][2] = 1;
        A[i][3] = 0;
        B[i] = dydx;
        Nconstraints++;
        return true;
}
double SplineClass::evaluate(double x)
{
        return a*x*x*x+b*x*x+c*x+d;
}