Difference between revisions of "File:Bessel8TestStep.jpg"

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Test of the 0-order [[discrete Bessel]] transform at the grid of 8 points with the step function
−
Importing image file
  
  +
  +
$f(x)=\mathrm{UnitStep}(2\!-\!x)$
  +
  +
shown with green line.
  +
  +
The discrete representation is shown with small red circles.
  +
  +
The [[Discrete Bessel]] transform is shown with big blue circles.
  +
  +
The exact [[Bessel transform]] is
  +
  +
$\displaystyle
  +
g(x)=\int_0^\infty J_0(xy) \, f(y)\, y \, \mathrm d y
  +
= \int_0^2 J_0(xy) \, y \, \mathrm d y
  +
=2J_1(2x)/x
  +
$
  +
  +
is shown with black curve.
  +
It shows qualitative agreement with the [[discrete Bessel]] transform, shown with circles.
  +
  +
==[[C++]] Generator of curves==
  +
<poem><nomathjax><nowiki>
  +
#include<math.h>
  +
#include<stdio.h>
  +
#include<stdlib.h>
  +
#define DB double
  +
#define DO(x,y) for(x=0;x<y;x++)
  +
DB jnp(int n,DB x){ return .5*( jn(n-1,x)-jn(n+1,x) ) ; } // Derivative of n th Bessel
  +
DB jnz(int v, int k){ DB x,t; t=M_PI*(k+.5*v-.25); x= t - (v*v-.25)*.5/t;
  +
x-= jn(v,x)/jnp(v,x); // Newton adjustment of the root
  +
x-= jn(v,x)/jnp(v,x);
  +
x-= jn(v,x)/jnp(v,x);
  +
return x; } // the k th zero of v th Bessel
  +
void ado(FILE *O, int X, int Y)
  +
{ fprintf(O,"%c!PS-Adobe-2.0 EPSF-2.0\n",'%');
  +
fprintf(O,"%c%cBoundingBox: 0 0 %d %d\n",'%','%',X,Y);
  +
fprintf(O,"/M {moveto} bind def\n");
  +
fprintf(O,"/L {lineto} bind def\n");
  +
fprintf(O,"/S {stroke} bind def\n");
  +
fprintf(O,"/s {show newpath} bind def\n");
  +
fprintf(O,"/C {closepath} bind def\n");
  +
fprintf(O,"/F {fill} bind def\n");
  +
fprintf(O,"/O {.04 0 360 arc C S} bind def\n");
  +
fprintf(O,"/o {.02 0 360 arc C S} bind def\n");
  +
fprintf(O,"/times-Roman findfont 20 scalefont setfont\n");
  +
fprintf(O,"/W {setlinewidth} bind def\n");
  +
fprintf(O,"/RGB {setrgbcolor} bind def\n");}
  +
//#include"ado.cin"
  +
  +
int main(){ int m,n,v,k; DB s, x,y; FILE *o;
  +
int M=8;
  +
DB X[M+1],W[M+1],T[M+1][M+1],TT[M+1][M+1], F[M],G[M];
  +
DB S=jnz(0,M+1);
  +
DB qs=sqrt(1./S);
  +
DB q=sqrt(2./S);
  +
for(n=1;n<M+1;n++){ x=jnz(0,n); X[n]=x*qs; y=W[n]=q/fabs(j1(x));
  +
printf("%3d %20.16lf %20.16lf\n",n,X[n],W[n]); }
  +
for(m=1;m<=M;m++){ printf("%2d",m); for(n=1;n<=M;n++){ T[m][n]=W[m]*j0(X[m]*X[n])*W[n]; }}
  +
for(m=1;m<=M;m++){printf("\n");
  +
for(n=1;n<=M;n++){printf("%14.10lf",T[m][n]); }}
  +
printf("\n");
  +
for(m=1;m<=M;m++){printf("\n");
  +
for(n=1;n<=M;n++){ s=0.;
  +
for(k=1;k<=M;k++) s+=T[m][k]*T[k][n] ;
  +
TT[m][n]=s;printf("%14.10lf",TT[m][n]);
  +
}}
  +
printf("\n\n");
  +
//for(m=1;m<=M;m++){x=X[m]; y=exp(-x*x/2.); F[m]=y*W[m]; printf("%14.10lf",F[m]); }
  +
for(m=1;m<=M;m++){x=X[m]; y=1.; if(x>2) y=0.; F[m]=y*W[m]; printf("%14.10lf",F[m]); }
  +
printf("\n");
  +
for(m=1;m<=M;m++){ s=0.; for(n=1;n<=M;n++) s+=T[m][n]*F[n];
  +
G[m]=s;}
  +
for(m=1;m<=M;m++) printf("%14.10lf",G[m]);
  +
printf("\n");
  +
//o=fopen("10.eps", "w"); ado(o,520,250);
  +
o=fopen("bessel8testSte.eps", "w"); ado(o,520,250);
  +
#define M(x,y) fprintf(o,"%8.4lf %8.4lf M\n",0.+x, 0.+y);
  +
#define L(x,y) fprintf(o,"%8.4lf %8.4lf L\n",0.+x, 0.+y);
  +
#define O(x,y) fprintf(o,"%8.4lf %8.4lf O\n",0.+x, 0.+y);
  +
#define o(x,y) fprintf(o,"%8.4lf %8.4lf o\n",0.+x, 0.+y);
  +
fprintf(o,"10 40 translate 100 100 scale\n");
  +
DO(n,6){M(n,2)L(n,0)}
  +
DO(n,5){M(0,n/2.)L(5,n/2.)}
  +
fprintf(o,"2 setlinecap 2 setlinejoin .006 W S\n");
  +
M(0,1)L(2,1)L(2,0)L(5,0)
  +
fprintf(o,"1 setlinecap 1 setlinejoin .012 W 0 .6 0 RGB S 0 0 0 RGB\n");
  +
//M(0,1) DO(n,500){x=.01*(n+1); y=exp(-x*x/2.); L(x,y)}
  +
//fprintf(o,"1 setlinecap 1 setlinejoin S\n");
  +
//DO(n,500){x=.01*(n+.1); y=2.*j1(2*x)/x;if(n==0) M(x,y) else L(x,y)}
  +
//fprintf(o,"1 setlinecap 1 setlinejoin S\n");
  +
M(0,2) DO(n,508){x=.01*(n+1); y=2.*j1(2*x)/x;L(x,y)} // strange..
  +
fprintf(o,"0 0 0 RGB .012 W S\n");
  +
fprintf(o,"1 0 0 RGB .016 W\n");
  +
for(m=1;m<=M;m++) o(X[m],F[m]/W[m])
  +
fprintf(o,"0 0 1 RGB .012 W\n");
  +
for(m=1;m<=M;m++) O(X[m],G[m]/W[m])
  +
fprintf(o,"showpage\n%c%cTrailer\n",'%','%'); fclose(o);
  +
system("epstopdf bessel8testSte.eps");
  +
system("open bessel8testSte.pdf");
  +
return 0;}
  +
</nowiki></nomathjax></poem>
  +
  +
==[[Latex]] Generator of labels==
  +
<poem><nomathjax><nowiki>
  +
\documentclass[12pt]{article}
  +
\usepackage{geometry}
  +
\usepackage{graphicx}
  +
\usepackage{rotating}
  +
\paperwidth 514pt
  +
\paperheight 234pt
  +
\topmargin -110pt
  +
\oddsidemargin -92pt
  +
\newcommand \ing {\includegraphics}
  +
\newcommand \sx {\scalebox}
  +
\newcommand \rot {\begin{rotate}}
  +
\newcommand \ero {\end{rotate}}
  +
\begin{document}
  +
\begin{picture}(410,248)
  +
\put(2,4){\ing{bessel8testSte}}
  +
\put(2,238){\sx{1.4}{$y$}}
  +
%\put(1,189){\sx{1.4}{$\frac 3 2$}}
  +
\put(2,139){\sx{1.4}{$1$}}
  +
%\put(1,89){\sx{1.4}{$\frac 1 2$}}
  +
\put(2,39){\sx{1.4}{0}}
  +
\put(10,30){\sx{1.4}{0}}
  +
\put(108,30){\sx{1.4}{1}}
  +
\put(208,30){\sx{1.4}{2}}
  +
\put(308,30){\sx{1.4}{3}}
  +
\put(409,30){\sx{1.4}{4}}
  +
\put(504,30){\sx{1.5}{$x$}}
  +
\put(123,114){\sx{1.4}{\rot{-52}$y\!=\! 2 J_1(2x)/x$\ero }}
  +
\put(184,141){\sx{1.2}{step }}
  +
\put(210,134){\sx{1.2}{\rot{-90}step\ero }}
  +
\end{picture}
  +
\end{document}
  +
</nowiki></nomathjax></poem>
  +
  +
==References==
  +
<references/>
  +
  +
[[Category:Bessel function]]
  +
[[Category:Bessel transform]]
  +
[[Category:C++]]
  +
[[Category:Discrete Bessel]]
  +
[[Category:Example]]
  +
[[Category:Explicit plot]]
  +
[[Category:Exponent]]
  +
[[Category:Latex]]
  +
[[Category:Makoto Morinaga]]

Latest revision as of 08:31, 1 December 2018

Test of the 0-order discrete Bessel transform at the grid of 8 points with the step function

$f(x)=\mathrm{UnitStep}(2\!-\!x)$

shown with green line.

The discrete representation is shown with small red circles.

The Discrete Bessel transform is shown with big blue circles.

The exact Bessel transform is

$\displaystyle g(x)=\int_0^\infty J_0(xy) \, f(y)\, y \, \mathrm d y = \int_0^2 J_0(xy) \, y \, \mathrm d y =2J_1(2x)/x $

is shown with black curve. It shows qualitative agreement with the discrete Bessel transform, shown with circles.

C++ Generator of curves


#include<math.h>
#include<stdio.h>
#include<stdlib.h>
#define DB double
#define DO(x,y) for(x=0;x<y;x++)
DB jnp(int n,DB x){ return .5*( jn(n-1,x)-jn(n+1,x) ) ; } // Derivative of n th Bessel
DB jnz(int v, int k){ DB x,t; t=M_PI*(k+.5*v-.25); x= t - (v*v-.25)*.5/t;
                x-= jn(v,x)/jnp(v,x); // Newton adjustment of the root
                x-= jn(v,x)/jnp(v,x);
                x-= jn(v,x)/jnp(v,x);
                return x; } // the k th zero of v th Bessel
void ado(FILE *O, int X, int Y)
{ fprintf(O,"%c!PS-Adobe-2.0 EPSF-2.0\n",'%');
        fprintf(O,"%c%cBoundingBox: 0 0 %d %d\n",'%','%',X,Y);
        fprintf(O,"/M {moveto} bind def\n");
        fprintf(O,"/L {lineto} bind def\n");
        fprintf(O,"/S {stroke} bind def\n");
        fprintf(O,"/s {show newpath} bind def\n");
        fprintf(O,"/C {closepath} bind def\n");
        fprintf(O,"/F {fill} bind def\n");
        fprintf(O,"/O {.04 0 360 arc C S} bind def\n");
        fprintf(O,"/o {.02 0 360 arc C S} bind def\n");
        fprintf(O,"/times-Roman findfont 20 scalefont setfont\n");
        fprintf(O,"/W {setlinewidth} bind def\n");
        fprintf(O,"/RGB {setrgbcolor} bind def\n");}
//#include"ado.cin"

int main(){ int m,n,v,k; DB s, x,y; FILE *o;
int M=8;
DB X[M+1],W[M+1],T[M+1][M+1],TT[M+1][M+1], F[M],G[M];
DB S=jnz(0,M+1);
DB qs=sqrt(1./S);
DB q=sqrt(2./S);
for(n=1;n<M+1;n++){ x=jnz(0,n); X[n]=x*qs; y=W[n]=q/fabs(j1(x));
                        printf("%3d %20.16lf %20.16lf\n",n,X[n],W[n]); }
for(m=1;m<=M;m++){ printf("%2d",m); for(n=1;n<=M;n++){ T[m][n]=W[m]*j0(X[m]*X[n])*W[n]; }}
for(m=1;m<=M;m++){printf("\n");
for(n=1;n<=M;n++){printf("%14.10lf",T[m][n]); }}
printf("\n");
for(m=1;m<=M;m++){printf("\n");
for(n=1;n<=M;n++){ s=0.;
                        for(k=1;k<=M;k++) s+=T[m][k]*T[k][n] ;
                        TT[m][n]=s;printf("%14.10lf",TT[m][n]);
                }}
printf("\n\n");
//for(m=1;m<=M;m++){x=X[m]; y=exp(-x*x/2.); F[m]=y*W[m]; printf("%14.10lf",F[m]); }
for(m=1;m<=M;m++){x=X[m]; y=1.; if(x>2) y=0.; F[m]=y*W[m]; printf("%14.10lf",F[m]); }
printf("\n");
for(m=1;m<=M;m++){ s=0.; for(n=1;n<=M;n++) s+=T[m][n]*F[n];
                 G[m]=s;}
for(m=1;m<=M;m++) printf("%14.10lf",G[m]);
printf("\n");
//o=fopen("10.eps", "w"); ado(o,520,250);
o=fopen("bessel8testSte.eps", "w"); ado(o,520,250);
#define M(x,y) fprintf(o,"%8.4lf %8.4lf M\n",0.+x, 0.+y);
#define L(x,y) fprintf(o,"%8.4lf %8.4lf L\n",0.+x, 0.+y);
#define O(x,y) fprintf(o,"%8.4lf %8.4lf O\n",0.+x, 0.+y);
#define o(x,y) fprintf(o,"%8.4lf %8.4lf o\n",0.+x, 0.+y);
fprintf(o,"10 40 translate 100 100 scale\n");
DO(n,6){M(n,2)L(n,0)}
DO(n,5){M(0,n/2.)L(5,n/2.)}
fprintf(o,"2 setlinecap 2 setlinejoin .006 W S\n");
M(0,1)L(2,1)L(2,0)L(5,0)
fprintf(o,"1 setlinecap 1 setlinejoin .012 W 0 .6 0 RGB S 0 0 0 RGB\n");
//M(0,1) DO(n,500){x=.01*(n+1); y=exp(-x*x/2.); L(x,y)}
//fprintf(o,"1 setlinecap 1 setlinejoin S\n");
//DO(n,500){x=.01*(n+.1); y=2.*j1(2*x)/x;if(n==0) M(x,y) else L(x,y)}
//fprintf(o,"1 setlinecap 1 setlinejoin S\n");
M(0,2) DO(n,508){x=.01*(n+1); y=2.*j1(2*x)/x;L(x,y)} // strange..
fprintf(o,"0 0 0 RGB .012 W S\n");
fprintf(o,"1 0 0 RGB .016 W\n");
for(m=1;m<=M;m++) o(X[m],F[m]/W[m])
fprintf(o,"0 0 1 RGB .012 W\n");
for(m=1;m<=M;m++) O(X[m],G[m]/W[m])
fprintf(o,"showpage\n%c%cTrailer\n",'%','%'); fclose(o);
system("epstopdf bessel8testSte.eps");
system("open bessel8testSte.pdf");
return 0;}

Latex Generator of labels


\documentclass[12pt]{article}
\usepackage{geometry}
\usepackage{graphicx}
\usepackage{rotating}
\paperwidth 514pt
\paperheight 234pt
\topmargin -110pt
\oddsidemargin -92pt
\newcommand \ing {\includegraphics}
\newcommand \sx {\scalebox}
\newcommand \rot {\begin{rotate}}
\newcommand \ero {\end{rotate}}
\begin{document}
\begin{picture}(410,248)
\put(2,4){\ing{bessel8testSte}}
\put(2,238){\sx{1.4}{$y$}}
%\put(1,189){\sx{1.4}{$\frac 3 2$}}
\put(2,139){\sx{1.4}{$1$}}
%\put(1,89){\sx{1.4}{$\frac 1 2$}}
\put(2,39){\sx{1.4}{0}}
\put(10,30){\sx{1.4}{0}}
\put(108,30){\sx{1.4}{1}}
\put(208,30){\sx{1.4}{2}}
\put(308,30){\sx{1.4}{3}}
\put(409,30){\sx{1.4}{4}}
\put(504,30){\sx{1.5}{$x$}}
\put(123,114){\sx{1.4}{\rot{-52}$y\!=\! 2 J_1(2x)/x$\ero }}
\put(184,141){\sx{1.2}{step }}
\put(210,134){\sx{1.2}{\rot{-90}step\ero }}
\end{picture}
\end{document}

References

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