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Thread Subject:
DFT ,Signal porcessing,fft,dft

Subject: DFT ,Signal porcessing,fft,dft

From: kk aKI

Date: 19 Feb, 2010 05:53:04

Message: 1 of 3

I am trying to write DFT code in form of

 X(f) = sum(k=1,N){ x(k) * exp(-2*pi*j*t(k)*f) }*deltat

where deltat=t(n+1)-t(n-1)/2, how can i write this.....

f=-(n/2-1:n/2-1)
for k=1:n
 X(f) = sum(k=1,N){ x(k) * exp(-2*pi*j*t(k)*f) }*deltat
end

Now here is the problem let
t=[1 2 3 [] 4 5 6 [] 9 10 [] []]
where [] denotes the missing samples..size of t is 1 by 8

how i can create deltat for all 8 positions....i am doing a reinmann sum method for calculating frequency spectra for irregular spaced samples

Thanks

Subject: DFT ,Signal porcessing,fft,dft

From: kk aKI

Date: 19 Feb, 2010 07:08:04

Message: 2 of 3


I think i need to draft my question in proper way i am trying to write DFT in following form


deltak=2pi/N*deltax
m=0:N-1

 X(f) = sum(n=0,N-1){ x(n) * exp(j*m*2pi/deltax*t(n) }*deltax_n

deltax=spacing in time domain
t(n)=sample locations
so assume that t=[ 1 2 3 4 5 6 7 8 12 13 14 15 18 19 20]
now deltax=1;
t(1)=1 & t(15)=20;

l_n=x_{n}+x_{n-1}/2; % mid point between two samples
deltax_n=l_{n+1}-l_{n}

This is applied for irregular sampling..........


Any idea how can i code it ! I am getting wrong result! can i use diff here for x_n.......

Thanks

kk








"kk aKI" <akikumar1983@gmail.com> wrote in message <hll900$a5k$1@fred.mathworks.com>...
> I am trying to write DFT code in form of
>
>
>
> where deltat=t(n+1)-t(n-1)/2, how can i write this.....
>
> f=-(n/2-1:n/2-1)
> for k=1:n
> X(f) = sum(k=1,N){ x(k) * exp(-2*pi*j*t(k)*f) }*deltat
> end
>
> Now here is the problem let
> t=[1 2 3 [] 4 5 6 [] 9 10 [] []]
> where [] denotes the missing samples..size of t is 1 by 8
>
> how i can create deltat for all 8 positions....i am doing a reinmann sum method for calculating frequency spectra for irregular spaced samples
>
> Thanks

Subject: DFT ,Signal porcessing,fft,dft, sampling

From: kk aKI

Date: 19 Feb, 2010 07:23:23

Message: 3 of 3



I think i need to draft my question in proper way i am trying to write DFT in following form
when i say that means frequency domain when i use x its mean time domain

deltak=2pi/N*deltax
m=0:N-1

 X(f) = sum(n=0,N-1){ x(n) * exp(j*m*2pi/deltax*x(n) }*deltax_n

deltax=spacing in time domain
x(n)=sample locations
so assume that x=[ 1 2 3 4 5 6 7 8 12 13 14 15 18 19 20]
now deltax=1;
x(1)=1 & x(15)=20;

l_n=x_{n}+x_{n-1}/2; % mid point between two samples
deltax_n=l_{n+1}-l_{n}

This is applied for irregular sampling..........


Any idea how can i code it ! I am getting wrong result! can i use diff here for x_n.......

Also it is given in the book that regular sampling in k or f implies periodic sampling in time.
x_{-1}=x_{N-1}-X;
x_{N}=x_{0}+X;
 
Where X=2pi/deltak and deltak=2pi/Ndeltax;

Now this time all details r correct ! this is algorithm given in book for irregular sampling .......I didnt get that line that regular sampling in f implies periodic sampling in time......also what will be deltax_{15}...i am not getting this...

Can any one help me in all this
Thanks

kk
"kk aKI" <akikumar1983@gmail.com> wrote in message <hlldck$k46$1@fred.mathworks.com>...
>
> I think i need to draft my question in proper way i am trying to write DFT in following form
>
>
> deltak=2pi/N*deltax
> m=0:N-1
>
> X(f) = sum(n=0,N-1){ x(n) * exp(j*m*2pi/deltax*t(n) }*deltax_n
>
> deltax=spacing in time domain
> t(n)=sample locations
> so assume that t=[ 1 2 3 4 5 6 7 8 12 13 14 15 18 19 20]
> now deltax=1;
> t(1)=1 & t(15)=20;
>
> l_n=x_{n}+x_{n-1}/2; % mid point between two samples
> deltax_n=l_{n+1}-l_{n}
>
> This is applied for irregular sampling..........
>
>
> Any idea how can i code it ! I am getting wrong result! can i use diff here for x_n.......
>
> Thanks
>
> kk
>
>
>
>
>
>
>
>
> "kk aKI" <akikumar1983@gmail.com> wrote in message <hll900$a5k$1@fred.mathworks.com>...
> > I am trying to write DFT code in form of
> >
> >
> >
> > where deltat=t(n+1)-t(n-1)/2, how can i write this.....
> >
> > f=-(n/2-1:n/2-1)
> > for k=1:n
> > X(f) = sum(k=1,N){ x(k) * exp(-2*pi*j*t(k)*f) }*deltat
> > end
> >
> > Now here is the problem let
> > t=[1 2 3 [] 4 5 6 [] 9 10 [] []]
> > where [] denotes the missing samples..size of t is 1 by 8
> >
> > how i can create deltat for all 8 positions....i am doing a reinmann sum method for calculating frequency spectra for irregular spaced samples
> >
> > Thanks

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