specgram and psd with complex valued data

Dear group

I am rather new to matplotlib. I have a reasonably large file of complex
valued data. Today I tried out specgram and psd, and they both work
nicely. However I would like the negative frequencies to be on the
negative side of the spectrum. I tried to look around, but could not
find any parameter to set this. My question is, if this is easily
possible or do I need to do something like

a,b,c,d=pylab.specgram(y,1024)
pylab.show()

x1,y1=a.shape
q=zeros([x1,y1],'d')
q[:,x1/2:x1-1]=a[:,0:x1/2-1]
q[:,0:x1/2-1]=a[:,x1-1:x1/2:-1]

pylab.imshow(q)

Apart from that I don't get the slicing to work properly yet, it would
be nicer if there was just a parameter to set for specgram

/Johan

I worked out the slicing

Pxx, freqs, bins = matplotlib.mlab.specgram(x, NFFT, Fs, detrend,
             window, noverlap) #line 3377

x1,y1=Pxx.shape
q=zeros([x1,y1],'d')
q[:][x1/2:x1]=Pxx[:][0:x1/2]
q[:][0:x1/2]=Pxx[:][x1/2:x1]
Pxx=q

This would be the small change needed. To me it looks like the change
could be done in axes.py

One could add an argument wrapparound=False
and then
if wrapparound
  new code

I assume that one should do something about the y-axis as well.
extent = xmin, xmax, -amax(b)/2, amax(b)/2, is probably not 100% OK but
will do it for me...

I guess I will have a look at psd now. I guess that will be easier

/Johan

···

On Wed, 2006-02-08 at 22:26 +0100, Johan Nilsson wrote:

Dear group

I am rather new to matplotlib. I have a reasonably large file of complex
valued data. Today I tried out specgram and psd, and they both work
nicely. However I would like the negative frequencies to be on the
negative side of the spectrum. I tried to look around, but could not
find any parameter to set this. My question is, if this is easily
possible or do I need to do something like

a,b,c,d=pylab.specgram(y,1024)
pylab.show()

x1,y1=a.shape
q=zeros([x1,y1],'d')
q[:,x1/2:x1-1]=a[:,0:x1/2-1]
q[:,0:x1/2-1]=a[:,x1-1:x1/2:-1]

pylab.imshow(q)

Apart from that I don't get the slicing to work properly yet, it would
be nicer if there was just a parameter to set for specgram

/Johan

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