[SciPy-dev] implementing IDL, Matlab, etc. functionality

Paul Barrett barrett at stsci.edu
Thu May 5 04:24:42 CDT 2005

Joe Harrington wrote:

>My main concern is not for coding labor but rather for numerical
>accuracy.  There are enough subtle differences between Python and IDL
>that hand-converting large amounts of numerical code would be
>error-prone.  For example, in Python the end of an array slice is one
>element beyond the end of an IDL slice.  An automatic converter would
>just add one to every slice's ending index.  A human wouldn't
>necessarily remember to do that every time, producing subtle bugs
>could be very hard to find in some cases.
This is my concern too.  In the case of IDL, most algorithms are 
implemented in single precision floating point.  The Python 
implementation by default would use double precision, unless we 
explicitly direct it to do otherwise.  This problem alone can cause much 
grief, because the IDL version is presumed to be the correct one, until 
demonstrated otherwise.  (I know this from personal experience.)  So in 
addition to the language being crappy, do we also want to propagate 
crappy (i.e. unstable) algorithms too?

 -- Paul

Paul Barrett, PhD      Space Telescope Science Institute
Phone: 410-338-4475    ESS/Science Software Branch
FAX:   410-338-4767    Baltimore, MD 21218

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