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Adding another form of polynomial

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Peter Boyle 2020-04-10 11:28:33 -04:00
parent 8e81a811d0
commit 3b0e07882f
1 changed files with 129 additions and 0 deletions
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Grid/algorithms/approx/JacobiPolynomial.h Normal file
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#ifndef GRID_JACOBIPOLYNOMIAL_H
#define GRID_JACOBIPOLYNOMIAL_H
#include <Grid/algorithms/LinearOperator.h>
NAMESPACE_BEGIN(Grid);
template<class Field>
class JacobiPolynomial : public OperatorFunction<Field> {
private:
using OperatorFunction<Field>::operator();
int order;
RealD hi;
RealD lo;
RealD alpha;
RealD beta;
public:
void csv(std::ostream &out){
csv(out,lo,hi);
}
void csv(std::ostream &out,RealD llo,RealD hhi){
RealD diff = hhi-llo;
RealD delta = diff*1.0e-5;
for (RealD x=llo-delta; x<=hhi; x+=delta) {
RealD f = approx(x);
out<< x<<" "<<f <<std::endl;
}
return;
}
JacobiPolynomial(){};
JacobiPolynomial(RealD _lo,RealD _hi,int _order,RealD _alpha, RealD _beta)
{
lo=_lo;
hi=_hi;
alpha=_alpha;
beta=_beta;
order=_order;
};
RealD approx(RealD x) // Convenience for plotting the approximation
{
RealD Tn;
RealD Tnm;
RealD Tnp;
RealD y=( x-0.5*(hi+lo))/(0.5*(hi-lo));
RealD T0=1.0;
RealD T1=(alpha-beta)*0.5+(alpha+beta+2.0)*0.5*y;
Tn =T1;
Tnm=T0;
for(int n=2;n<=order;n++){
RealD cnp = 2.0*n*(n+alpha+beta)*(2.0*n-2.0+alpha+beta);
RealD cny = (2.0*n-2.0+alpha+beta)*(2.0*n-1.0+alpha+beta)*(2.0*n+alpha+beta);
RealD cn1 = (2.0*n+alpha+beta-1.0)*(alpha*alpha-beta*beta);
RealD cnm = - 2.0*(n+alpha-1.0)*(n+beta-1.0)*(2.0*n+alpha+beta);
Tnp= ( cny * y *Tn + cn1 * Tn + cnm * Tnm )/ cnp;
Tnm=Tn;
Tn =Tnp;
}
return Tnp;
};
// Implement the required interface
void operator() (LinearOperatorBase<Field> &Linop, const Field &in, Field &out) {
GridBase *grid=in.Grid();
int vol=grid->gSites();
Field T0(grid);
Field T1(grid);
Field T2(grid);
Field y(grid);
Field *Tnm = &T0;
Field *Tn = &T1;
Field *Tnp = &T2;
// RealD T0=1.0;
T0=in;
// RealD y=( x-0.5*(hi+lo))/(0.5*(hi-lo));
// = x * 2/(hi-lo) - (hi+lo)/(hi-lo)
Linop.HermOp(T0,y);
RealD xscale = 2.0/(hi-lo);
RealD mscale = -(hi+lo)/(hi-lo);
Linop.HermOp(T0,y);
y=y*xscale+in*mscale;
// RealD T1=(alpha-beta)*0.5+(alpha+beta+2.0)*0.5*y;
RealD halfAmB = (alpha-beta)*0.5;
RealD halfApBp2= (alpha+beta+2.0)*0.5;
T1 = halfAmB * in + halfApBp2*y;
for(int n=2;n<=order;n++){
Linop.HermOp(*Tn,y);
y=xscale*y+mscale*(*Tn);
RealD cnp = 2.0*n*(n+alpha+beta)*(2.0*n-2.0+alpha+beta);
RealD cny = (2.0*n-2.0+alpha+beta)*(2.0*n-1.0+alpha+beta)*(2.0*n+alpha+beta);
RealD cn1 = (2.0*n+alpha+beta-1.0)*(alpha*alpha-beta*beta);
RealD cnm = - 2.0*(n+alpha-1.0)*(n+beta-1.0)*(2.0*n+alpha+beta);
// Tnp= ( cny * y *Tn + cn1 * Tn + cnm * Tnm )/ cnp;
cny=cny/cnp;
cn1=cn1/cnp;
cn1=cn1/cnp;
cnm=cnm/cnp;
*Tnp=cny*y + cn1 *(*Tn) + cnm * (*Tnm);
// Cycle pointers to avoid copies
Field *swizzle = Tnm;
Tnm =Tn;
Tn =Tnp;
Tnp =swizzle;
}
out=*Tnp;
}
};
NAMESPACE_END(Grid);
#endif