Why is cohere function in matplotlib (python) give answer different from mscohere function in MATLAB? -

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in maltlab , pythonmatplotlib.mlab contains numerical python functions written compatability matlab commands same names.

  1. but me different results in matlab , python. has idea, why so?

  2. matlab mscohere function has parameter window set size of window, not find cohere function in matplotlib.mlab (python)

    cxy = mscohere(y1,y2,16,0,16)

    cxy = matplotlib.pyplot.cohere(y1, y2,nfft=16,noverlap=0)

where y1 , y2 same in matlab , python , of length 1024

any help?

here code:

matlab:

fs=8000; y1=zeros(1,1024); y2=zeros(1,1024); f =0:100:1900     n=0:1023       y1(n+1)=y1(n+1)+sin(2*pi*f*n/fs);       if mod(f,200)==0           y2(n+1)=y2(n+1)+sin(2*pi*f*n/fs);       end     end end  cxy = mscohere(y1,y2,16,0,16); display(cxy);  cxy =      0.8300     0.0504     0.0006     0.0082     0.1828     0.2562     0.7984     0.9788     0.9884

python:

fs=8000 sample=1024 frequencys=100 * np.arange(20) #print(frequencys)  y1=np.zeros(sample) y2=np.zeros(sample) f in range(frequencys.size):     n in range(sample):         y1[n]=y1[n]+sin(2*pi*frequencys[f]*n/fs)         if frequencys[f]%200==0:             y2[n]=y2[n]+sin(2*pi*frequencys[f]*n/fs) cxy,f = plt.cohere(y1, y2,nfft=16,noverlap=0) print(cxy)      cxy=[ 0.78894285   0.06083255   0.01161213   0.00249976   0.14194519   0.38694284  0.78120729   0.8384586    0.85438165]

originally matplotlib.mlab functions meant provide similar capabilities matlab equivalents, basics approaches between matlab , numpy differ don't things in same way, , in cases have diverged due differing needs and/or goals. nowadays mlab more set of numerical functions aren't available in numpy needed matplotlib.

in case, matlab function defaults using hamming window, while matplotlib version defaults using hanning window. can reproduce matlab results simple passing appropriately-lengthed hamming window. also, matlab uses fs=1 default while matplotlib uses fs=2 default, think changes frequencies, not cxy:

>>> cxy, _ = mlab.cohere(y1, y2, window=np.hamming(16), nfft=16, noverlap=0, fs=1) >>> print(cxy) [  8.29985202e-01   5.03649611e-02   5.54167037e-04   8.19190824e-03   1.82760544e-01   2.56179777e-01   7.98391906e-01   9.78827021e-01   9.88429511e-01]

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