i copied it from the book i know the error is in the omega definition(line 12) but i dont know how to solve it please help

clear all;
distance=15;
beta2=1;
N=1;
mshape=input('m=0 for seech, m>0 for super-gaussian= ');
chirp0=0;
nt=1024;tmax=32;
stepnum=round(20*distance*N.^2);
deltaz=distance/stepnum;
dtau=(2*tmax)/nt;
tau=(-nt/2:nt/2-1)*dtau;

    omega=(pi/tmax)*(0:nt/2-1) (-nt/2:-1);
  if mshape==0
      uu=sech(tau).*exp(-0.5i*chirp0*tau.^2);
  else
      uu=exp(-0.5*(1+1i*chirp0).*tau.^(2*mshape));
  end
  %%%%%
  temp=fftshift(ifft(uu)).*(nt*dtau)/sqrt(2*pi);
  figure;
  subplot(2,1,1);
  plot(tau,abs(uu).^2,'--k');hold on;
  axis([-5 5 0 inf]);
  xlabel('time');
  ylabel('power');
  title('input and output pulse shape and spectrum');
  subplot(2,1,2);
  plot(fftshift(omega)/(2*pi),abs(temp).^2,'--k');hold on;
  axis([-.5 .5 0 inf]);
  xlabel('frequency');
  ylabel('power');
  %%%%%
  dispersion=exp(0.5*1i*beta2*omega.^2*delta2);
  hhz=1i*N^2*deltaz;
  %%%%%
  temp=uu.*exp(abs(uu).^2.*hhz/2);
  for n=1:stepnum
      ftemp=ifft(temp).*dispersion;
      uu=fft(f_temp);
      temp=uu.*exp(abs(uu).^2.*hhz);
  end
  uu=temp.*exp(-abs(uu).^2.*hhz);
  temp=fftshift(ifft(uu)).*(nt*dtau)/sqrt(2*pi);
  subplot(2,1,1)
  plot(tau,abs(uu).^2,'-k')
  subplot(2,1,2)
  plot(fftshift(omega)/(2*pi),abs(temp).^2,'-k')

[Walter Roberson]

Which book did you copy it from?

Perhaps you could post an image of the equations ?

[abed]

the famous book Non-linear fiber optics done by Agrawal the equation is call the non-linear Schroedinger equation

[Walter Roberson]

This code is from the book? Could you post an image of how the omega line shows up in the code in the book?

[abed]

[anu chauhan]

plot((fftshift*omega/(2*pi)),abs(temp).^2,'k');hold on;

i am facing error with this comment in above code can anyone help, its error commenting that vectors must be of same length

[Walter Roberson]

anu chauhan,

You have put at least one |(| in the wrong place. You have somehow made fftshift into a reference to a variable instead of making it a call to the MATLAB fftshift function. Perhaps

plot(fftshift(omega/(2*pi)), abs(temp).^2, 'k')

[Afroja Akter]

Hi ,

I solve this problem in Matlab, but my problem is when i try to solve in Fortran95. Could anybody help me in fft loop portion solution in fortran.

Thanking Afroja

Answer 1

[Wayne King]

I'm assuming that you are missing brackets around the vector in omega

 distance=15;
 beta2 = 1;
delta2=1;
N=1;
mshape=input('m=0 for seech, m>0 for super-gaussian= ');
chirp0=0;
nt=1024;tmax=32;
stepnum=round(20*distance*N.^2);
deltaz=distance/stepnum;
dtau=(2*tmax)/nt;
tau=(-nt/2:nt/2-1)*dtau;

    omega=(pi/tmax)*[(0:nt/2-1) (-nt/2:-1)];
  if mshape==0
      uu=sech(tau).*exp(-0.5i*chirp0*tau.^2);
  else
      uu=exp(-0.5*(1+1i*chirp0).*tau.^(2*mshape));
  end
  %%%%%
  temp=fftshift(ifft(uu)).*(nt*dtau)/sqrt(2*pi);
  figure;
  subplot(2,1,1);
  plot(tau,abs(uu).^2,'--k');hold on;
  axis([-5 5 0 inf]);
  xlabel('time');
  ylabel('power');
  title('input and output pulse shape and spectrum');
  subplot(2,1,2);
  plot(fftshift(omega)/(2*pi),abs(temp).^2,'--k');hold on;
  axis([-.5 .5 0 inf]);
  xlabel('frequency');
  ylabel('power');
  %%%%%
  dispersion=exp(0.5*1i*beta2*omega.^2*delta2);
  hhz=1i*N^2*deltaz;
  %%%%%
  temp=uu.*exp(abs(uu).^2.*hhz/2);
  for n=1:stepnum
      ftemp=ifft(temp).*dispersion;
      uu=fft(ftemp);
      temp=uu.*exp(abs(uu).^2.*hhz);
  end
  uu=temp.*exp(-abs(uu).^2.*hhz);
  temp=fftshift(ifft(uu)).*(nt*dtau)/sqrt(2*pi);
  subplot(2,1,1)
  plot(tau,abs(uu).^2,'-k')
  subplot(2,1,2)
  plot(fftshift(omega)/(2*pi),abs(temp).^2,'-k')

However there are other problems, nowhere do you define/compute what delta2 is. I have just set it equal to 1, but I have no idea, you'll have to figure that part out.

Also, there is mistake where f_temp is confused with ftemp.