The Instantaneous Frequencies from IMF Aren't Consistent with Its Spectrum

Question

I'm trying to find the instantaneous frequencies for one of the Intrinsic Mode Functions (IMFs) I extracted from the original signal using Hilbert-Huang Transform. So, I got the following spectrum for that IMF:

However, when I tried to get the instantaneous frequencies for this IMF, I got the following (I'm using this library):

[x,_]=inst_freq(imfs[0])
x*fs
Out[17]: 
array([100., 200., 100., 100., 200., 200., 100., 100., 100., 100., 100.,
       100., 100., 100., 100., 100., 100., 100., 200., 100., 100., 100.,
       100., 100., 100., 100., 100., 200., 100., 100., 200., 100., 100.,
       100., 200., 100., 200., 100., 100., 100., 100., 200., 200., 200.,
       100., 200., 100., 100., 100., 100., 100., 100., 100., 100., 100.,
       100., 100., 100., 100., 200., 100., 100., 200., 100., 100., 100.,
       200., 100., 200., 200., 100., 100., 200., 100., 100., 100., 100.,
       100., 100., 200., 100., 100., 100., 100., 100., 100., 200., 200.,
       200., 100., 100., 200., 100., 100., 100., 100., 200., 100., 100.,
       100., 100., 100., 100., 200., 100., 100., 200., 200., 100., 100.,
       100., 100., 200., 100., 100., 100., 100., 100., 100., 200., 200.,
       100., 100., 100., 200., 100., 100., 100., 200., 200., 200., 100.,
       100., 200., 200., 100., 100., 100., 100., 200., 100., 100., 100.,
       100., 100., 100., 200., 200., 200., 100., 100., 200., 200., 200.,
       100., 100., 100., 100.])

From the instantaneous frequencies, one could imagine that the spectrum contains only the 100 and 200 Hz frequencies. Am I missing something here?

Answer 1

This is a major bug in this library. see http://github.com/jaidevd/pyhht/issues/43#issuecomment-398388106 I think it's better to use more robust libraries that are well-tested.