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MathGroup Archive 1995

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Re: Re: Re: Bug in interpretation of mma Series[] command?

  • To: mathgroup at
  • Subject: [mg2371] Re: [mg2287] Re: [mg2268] Re: Bug in interpretation of mma Series[] command?
  • From: siegman at (A. E. Siegman)
  • Date: Sun, 29 Oct 1995 22:48:46 -0500
  • Organization: Stanford University

As the original complainant on this topic, I'd just like to reiterate two
quick points in the discussion of why having

      f1[x] * Series[f2[x]]

evaluate to

      Series[f1[x] * f2[x]]

(rather than remain unevaluated, for example, or do something, anything,
else) still seems to me a bad thing.

1)  It's _grossly_ unusual or unfamiliar behavior:

I'd challenge the Wolfram (or other) respondents on this issue to name any
other common situation where

   f1 * Operator[f2]

is _expected_ by a user to behave as  Operator[f1 * f2]  (or maybe 
Operator[f1] * Operator[f2]), with Operator[] being an operator that
really does something to the f's.  The [] symbols are just widely
understood to mark the bounds of what (any)  Operator[]  operates on.

2)  It can lead to, indeed promotes, _large_ undetected errors:

If I understand the situation (and I've missed some of the messages), the
unwanted action is essentially a forced type conversion in combining  f1 
and  Series[f2] .  I think even the relatively unsophisticated user may
understand that if one multiplies or adds an integer and a real there may
be a forced conversion of the product to real, and a small loss of
accuracy.  But this loss in accuracy is normally both small and also of
small import, though it may, of course, be very important in certain rare

But a forced (and unnoted) series expansion of  f1  is _likely_ to lead to
_large_ inaccuracies, since the above input is most likely to be used
precisely in situations where  Series[f2] is appropriate and acceptable,
but  Series[f1]  is NOT (which is why f1 was left outside in the first


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