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ID  Category  Severity  Reproducibility  Date Submitted  Last Update  
0000519  [ALGLIB] Spec.functions  major  always  20130423 17:24  20180102 17:23  
Reporter  zaytsev  View Status  public  
Assigned To  SergeyB  
Priority  normal  Resolution  open  
Status  assigned  Product Version  3.7.0  
Summary  0000519: Exponential integral Ei(x) returns 0 for x <= 0  
Description 
The Ei(x) in ALGLIB returns 0 for all x <= 0 . This is not documented on the website: http://www.alglib.net/specialfunctions/exponentialintegrals.php In the source code, however, it says "Not defined for x <= 0", which, of course, explains this behavior, but doesn't really help. Anyways, the function Ei(x) is defined on all real axis [1] and I see no reason why you would silently return 0 for x <= 0, while many other special function packages allow one to compute Ei(x) for negative arguments. I need fast and accurate routines to compute the exponential integrals and would highly appreciate if you could address this problem. Thanks! [1]: http://mathworld.wolfram.com/ExponentialIntegral.html 

Additional Information  I'm looking specifically at the C/C++ version of ALGLIB, but it shouldn't really matter.  
Programming language  All  
Attached Files  

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