[SciPy-user] S.stats broken?

Robert Kern rkern at ucsd.edu
Mon Jun 20 15:41:55 CDT 2005

Stephen Walton wrote:
> In the below, I've done "import scipy as S" and "import scipy.special as 
> special"
> In [272]:S.stats.norm.cdf(0,-4.)
> Out[272]:0.999999713348

In [5]: stats.norm.cdf(-4.)
Out[5]: 3.16712418331e-05

The value you want to evaluate at comes first. Location and scale or any 
other such parameters come after.

> In [273]:special.ndtr(-4.)
> Out[273]:3.1671241833119884e-05
> If I'm reading the code correctly, S.stats.norm.cdf(0,-4) should be 
> equal to special.ndtr(-4).  It is not.  Why?
> lognorm.cdf is even worse.  S.stats.lognorm.cdf(1,x) returns 0.5 for any 
> value of x from a small value up to and including inf.

Same here. You want scipy.stats.lognorm(x, 1).

> What am I missing here?  This package can't possibly be this badly 
> broken.  scipy.__version__ is 0.3.3_309.4624.

Robert Kern
rkern at ucsd.edu

"In the fields of hell where the grass grows high
  Are the graves of dreams allowed to die."
   -- Richard Harter

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