mirror of
https://github.com/paboyle/Grid.git
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104 lines
2.8 KiB
C++
104 lines
2.8 KiB
C++
#include <Grid.h>
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using namespace std;
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using namespace Grid;
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using namespace Grid::QCD;
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class MultiShiftFunction {
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public:
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std::vector<double> poles;
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std::vector<double> residues;
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double norm;
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double lo,hi;
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MultiShiftFunction(int n,double _lo,double _hi): poles(n), residues(n), lo(_lo), hi(_hi) {;};
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double approx(double x);
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void csv(std::ostream &out);
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void gnuplot(std::ostream &out);
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};
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double MultiShiftFunction::approx(double x)
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{
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double a = norm;
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for(int n=0;n<poles.size();n++){
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a = a + residues[n]/(x+poles[n]);
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}
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return a;
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}
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void MultiShiftFunction::gnuplot(std::ostream &out)
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{
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out<<"f(x) = "<<norm<<"";
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for(int n=0;n<poles.size();n++){
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out<<"+("<<residues[n]<<"/(x+"<<poles[n]<<"))";
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}
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out<<";"<<std::endl;
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}
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void MultiShiftFunction::csv(std::ostream &out)
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{
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for (double x=lo; x<hi; x*=1.05) {
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double f = approx(x);
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double r = std::sqrt(x);
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out<< x<<","<<r<<","<<f<<","<<r-f<<std::endl;
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}
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return;
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}
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int main (int argc, char ** argv)
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{
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Grid_init(&argc,&argv);
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std::cout << "Testing Remez"<<std::endl;
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double lo=0.01;
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double hi=1.0;
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int precision=64;
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int degree=10;
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AlgRemez remez(0.001,1.0,precision);
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////////////////////////////////////////
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// sqrt and inverse sqrt
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////////////////////////////////////////
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MultiShiftFunction Sqrt(degree,lo,hi);
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MultiShiftFunction InvSqrt(degree,lo,hi);
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MultiShiftFunction SqrtSqrt(degree,lo,hi);
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MultiShiftFunction InvSqrtSqrt(degree,lo,hi);
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std::cout << "Generating degree "<<degree<<" for x^(1/2)"<<std::endl;
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remez.generateApprox(degree,1,2);
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remez.getPFE (& Sqrt.residues[0],& Sqrt.poles[0],& Sqrt.norm);
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remez.getIPFE(&InvSqrt.residues[0],&InvSqrt.poles[0],&InvSqrt.norm);
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std::cout << "Generating degree "<<degree<<" for x^(1/4)"<<std::endl;
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remez.generateApprox(degree,1,4);
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remez.getPFE (&SqrtSqrt.residues[0],&SqrtSqrt.poles[0],&SqrtSqrt.norm);
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remez.getIPFE(&InvSqrtSqrt.residues[0],&InvSqrtSqrt.poles[0],&InvSqrtSqrt.norm);
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ofstream gnuplot(std::string("Sqrt.gnu"),std::ios::out|std::ios::trunc);
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Sqrt.gnuplot(gnuplot);
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ofstream gnuplot_inv(std::string("InvSqrt.gnu"),std::ios::out|std::ios::trunc);
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InvSqrt.gnuplot(gnuplot);
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double x=0.6789;
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double sx=std::sqrt(x);
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double ssx=std::sqrt(sx);
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double isx=1.0/sx;
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double issx=1.0/ssx;
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double asx =Sqrt.approx(x);
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double assx =SqrtSqrt.approx(x);
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double aisx =InvSqrt.approx(x);
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double aissx=InvSqrtSqrt.approx(x);
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std::cout << "x^(1/2) : "<<sx<<" "<<asx<<std::endl;
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std::cout << "x^(1/4) : "<<ssx<<" "<<assx<<std::endl;
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std::cout << "x^(-1/2): "<<isx<<" "<<aisx<<std::endl;
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std::cout << "x^(-1/4): "<<issx<<" "<<aissx<<std::endl;
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assert(fabs(sx-asx)<1.0e-6);
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assert(fabs(ssx-assx)<1.0e-6);
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assert(fabs(isx-aisx)<1.0e-6);
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assert(fabs(issx-aissx)<1.0e-6);
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Grid_finalize();
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}
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