[seqfan] Re: Futurevalue considered harmful
dwilson at gambitcomm.com
Mon Aug 24 18:46:51 CEST 2009
I've been listening to this thread, and here is my considered opinion,
which I will express this once:
A domain-specific formula for an OEIS sequence should lend the sequence
a domain-specific meaning. If it does not, it is nothing but obfuscation.
For example, let's look at
%p A000079 with(finance):seq(futurevalue(2,1,n), n=-1..31);# [From
Zerinvary Lajos (zerinvarylajos(AT)yahoo.com), Mar 24 2009]
This, says that 2 dollars lent at 100% for n-1 years yields A000079(n)
dollars. This is true, but I probably would have used a(n) =
futurevalue(1, 1, n), n=0..32 instead, i.e, 1 dollar lent at 100% for n
years yields A000079(n) = 2^n dollars.
But my point is, this formula reflects a legitimate financial
interpretation of A000079(n), as opposed to
%p A000217 with(finance):seq(add(futurevalue(k,3,2),k=0..n)/16,n=0..55);
- Zerinvary Lajos (zerinvarylajos(AT)yahoo.com), Jun 20 2008
which is nothing but obfuscation. futurevalue(k,3,2) is an obfuscation
for 16n, so that the equation is really A000027(n) = SUM(k = 0..n;
16n/16) = SUM(k = 0..n; n) = already known. This formula does not
suggest a financial interpretation for A000217, it simply complicates a
known formula, and should be elided. Inclusion of such formulae make the
OEIS look sophomoric, certainly not up to professional standards.
I could just as easily take any
%F A123456 a(n) = formula(n)
%p A123456 with(finance):seq(futurevalue(2,1,n)*formula(n)/16n, n=0..20);
and make the sequence into a financial sequence.
So, in short, I disagree both with the decision to elide all
with(finance) sequences, and with the decision to retain them all. They
should be evaluated individually, and the obfuscatory ones (which I
suspect are most), should be elided. The author, IMHO, is mathematically
unsophisticated or else has an agenda, and future submissions from that
author should be severely scrutinized before admission.
Raff, Paul wrote:
>> Incidentally, someone (I've lost track of who) made the comment (I'm
>> paraphrasing) that business analysts aren't very sophisticated
>> mathematically, and might use an expression like futurevalue(x,2,2)
>> without realizing that this is the same as 9*x.
> I believe it was me who said that comment, and I just wanted to clarify,
> since that definitely wasn't my intent. I was simply trying to mention that
> they speak in a different language that we do, and I would wager that some
> of them would get the idea quicker told in a future value context than with
> straight-up mathematics.
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