[Numpy-discussion] QQ Plot in Python and Noncentral Chisquare

josef.pktd at gmail.com josef.pktd at gmail.com
Wed Aug 15 21:59:12 EDT 2012

On Wed, Aug 15, 2012 at 10:59 AM, Yi, Chuang
<chuang.yi at bankofamerica.com> wrote:
> Hello,
> I am a new user of Python. I have a couple of questions that would
> appreciate your guidance!
> QQ Plot in Python: I could not find any functions in either Numpy or Scipy
> to do QQ Plot of two vectors of data. For example, in Matlab, one could just
> call qqplot(X,Y), which will generate the QQ plot of vector X against vector
> Y. Would you please let me know which python package has similar
> functionality?
> Noncentral Chisquare: it looks to me that in Numpy and Scipy, the noncentral
> chisquare distribution only allows Integer degree of freedom. For example,
> the following code will produce an error message. In R, however, it also
> allows non-integer degree of freedom. Would you please let me know which
> python package has similar functionality?
> data = numpy.random.noncentral_chisquare(0.5, 2, 100)
> ValueError: df <= 0

restriction is >1 not integer

>>> np.random.noncentral_chisquare(1, 2, 100)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "mtrand.pyx", line 1957, in
ValueError: df <= 0

>>> np.random.noncentral_chisquare(1.0001, 2, 100)
array([  5.75083221,   1.08050491,   0.69267684,   1.37806056,
         2.39899   ,   0.31415666,   2.9202386

I don't know if the >1 restriction is justified or could be dropped.


> Thank you very much,
> Regards,
> Chuang
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