[seqfan] Re: Futurevalue considered harmful

David Wilson 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)

and add

%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.
>             [paul]
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