Re: postgres arithmetic: raising to nth power

From: Ennio-Sr pgsql-novice(at)postgresql(dot)org Re: postgres arithmetic: raising to nth power 2005-09-30 00:05:59 20050930000559.GB8506@deby.ei.hnet (view raw or whole thread) 2005-09-29 19:36:57 from Ennio-Sr  2005-09-29 22:27:24 from Tom Lane   2005-09-30 00:05:59 from Ennio-Sr  2005-09-29 22:34:45 from Andrej Ricnik-Bay   2005-09-29 23:26:27 from Ennio-Sr pgsql-novice
```* Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> [290905, 18:27]:
> Ennio-Sr <nasr(dot)laili(at)tin(dot)it> writes:
> > So, the problem is: how can I get to know which results are correct and
> > which aren't?  May be the presence on the trailing 'e+..' is signalling
> > there is an error?
>
> I take it you've never seen floating-point notation before?
>
> Read the "e" as "times ten to the power of".
>
> 			regards, tom lane

Touche' .... :-)

Of course, I did see floating-point notation before, but that doesn't
mean I recalled how I should interpret it .... ;)
[I left school many, many, many, many, many years ago and could not find
my old financial maths book yet!]

Back to my problem, rivisited at the light of your (formerly obscure to me ;) )
'clarification':

1 - select 100*(1.10)^1277
----------------------
7.21869922862002e+54
^^
2 - select (1.10)^1277
----------------------
7.21869922862002e+52
^^
I should have noticed the difference in the 'trailing numbers' ... but I
was diverted by other problems .....;(

§§§§§§§§§§§§§§§§

# Suppose I invest one dollar at a 10% compound rate for a period of 3
# years; at the end I should get :

select (1+.10)^3
-----------------
1.331

# Now the reverse: what is the IRR on my investment considered that I
# got  \$ 1.331 after a 3 years period?

select (1.331)^(1/3::float)-1
-------------------------------
0.1

# or, to get a finer result:

select to_char( (1.331)^(1/3::float)-1,'9999.0000' )
------------------------------------------------------
.1000
(1 row)
§§§§§§§§§§§§§§§§§§

Thanks again.
Regards,
Ennio.

--
[Perche' usare Win\$ozz (dico io) se ..."anche uno sciocco sa farlo.   \\?//
Fa' qualche cosa di cui non sei capace!"  (diceva Henry Miller) ]    (°|°)
[Why use Win\$ozz (I say) if ... "even a fool can do that.              )=(
Do something you aren't good at!" (as Henry Miller used to say) ]

```

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