#include "math_bspline.h"

#include <cstdlib>

#include <assert.h>

namespace ModuleBase

{

Bspline::Bspline()

{

bezier = nullptr;

norder = 0;

xi = 0;

Dx = 1.0;

}

Bspline::~Bspline()

{

if(bezier!=nullptr) delete[] bezier;

}

void Bspline::init(int norderin, double Dxin, double xiin)

{

this->xi = xiin;

this->Dx = Dxin;

this->norder = norderin;

assert(Dx > 0);

//norder must be a positive even number.

assert(norder > 0);

assert(norder % 2 == 0);

bezier = new double [this->norder+1];

for(int i = 0 ; i < norder+1 ; ++i)

{

bezier[i] = 0;

}

}

double Bspline::bezier_ele(int n)

{

return this->bezier[n];

}

void Bspline::getbspline(double x)

{

bezier[0] = 1.0;

for(int k = 1 ; k <= norder ; ++k)

{

//for n>=1

for(int n = k; n >= 1; --n )

{

this->bezier[n] = ((x + n*this->Dx - this->xi)*this->bezier[n] +

(this->xi + (k-n+1)*Dx - x)*this->bezier[n-1])/(k*this->Dx);

}

//for n = 0

this->bezier[0] = (x - this->xi)*this->bezier[0] / (k*this->Dx);

}

}

}