DFT problem

1. Feb 28, 2012

souhal.67

I have a f(n*t) vs t data areay how to find out its (DFT) fourier transform in c. I find every time that every program needs its real and imaginarry part. but i have only magnitude. please help me out to find DFT of these data .

2. Feb 29, 2012

sophiecentaur

If your data is all real then why not put the imaginary values as zero?

3. Mar 3, 2012

souhal.67

then how i get the value of omega for ploting

4. Mar 3, 2012

souhal.67

after sampling I have value of t & X(t) like
375.020000 -0.754661
375.030000 -0.755227
375.040000 -0.755841
375.050000 -0.756501
375.060000 -0.757207
375.070000 -0.757960
375.080000 -0.758759
375.090000 -0.759604
375.100000 -0.760494
375.110000 -0.761431
375.120000 -0.762414
375.130000 -0.763442
375.140000 -0.764515
375.150000 -0.765633
375.160000 -0.766797
375.170000 -0.768005
375.180000 -0.769258
I would like to find DFT and I need omega/freq and X(W) value

5. Mar 3, 2012

souhal.67

after sampling I have value of t & X(t) like
375.020000 -0.754661
375.030000 -0.755227
375.040000 -0.755841
375.050000 -0.756501
375.060000 -0.757207
375.070000 -0.757960
375.080000 -0.758759
375.090000 -0.759604
375.100000 -0.760494
375.110000 -0.761431
375.120000 -0.762414
375.130000 -0.763442
375.140000 -0.764515
375.150000 -0.765633
375.160000 -0.766797
375.170000 -0.768005
375.180000 -0.769258
I would like to find DFT and I need omega/freq and X(W) value

6. Mar 3, 2012

sophiecentaur

How much do you know about discrete Fourier transforms? What are you trying to find out from the data?

7. Mar 3, 2012

souhal.67

Thank you for reply. I want to find out a frequency Vs Amplitude graph

8. Mar 3, 2012

souhal.67

I want to find out time vs Amplitude to frequency vs Amplitude of a signal

9. Mar 3, 2012

sophiecentaur

And what does DFT do? (I want you to work a bit for this. ;-) )

10. Mar 3, 2012

souhal.67

I have a collage project and I have a system out put I must make a program to find out system's frequency response of numerically.

11. Mar 3, 2012

sophiecentaur

You didn't say what the DFT does. You have asked a question that suggests you have no idea. I could tell you anything and you would believe me. You need to understand about the process.
If you want an answer then put some data in for a familiar waveform for which you know the frequency spectrum. Try some sine waves with different periods.