ODFF: yet more suggestions

["David King" <openoffice@drking.plus.com>]

Hello all
Another list for the archive...

PMT
* Constraints should have Nper>0 and integer
* For clarity, should specify that with PayType=1 the first payment is 
made on 
the same day the loan is taken out. 
* The formula is unstable at very low rates. Better to use an 
approximation - 
but Calc at least does not do so, and will produce #VALUE! errors. Excel 
97 
similarly gives #DIV/0!

CORREL
Currently as defined, also allows different dimensions for the two 
parameters - if this is intended should be explicitly stated (NB Calc 
expects the same 
dims). Also it's a redundant function - it's identical to Pearson.

PV
Payment can be omitted if fv is given.

DISC
should divide by YEARFRAC, not multiply I think.

SYD
"sum-of-years' digits method"
*This phrase appears to be copied from Excel. I'd suggest either "sum-
of-years'
digits method" or "sum of years'-digits method". 
* Formula is at:
http://wiki.services.openoffice.org/w/index.php?title=Documentation/How_
Tos/Calc
:_SYD_function

DDB
"I don't know how to put this into the equations."
See:
http://wiki.services.openoffice.org/wiki/Documentation/How_Tos/Calc:_DDB
_functio
n

DOLLARDE
Does not return currency; returns a number.

TBILLEQ
* Excel gives the formula:
"TBILLEQ is calculated as TBILLEQ = (365 x rate)/360-(rate x DSM), where 
DSM is
the number of days between settlement and maturity computed according to 
the 
360 days per year basis."
That's wrong - should be (365 x rate)/[360-(rate x DSM)]. Also: using 
the 360 
day year is vital information which needs to be included.
* "bond-equivalent yield for a treasury bill" is probably lifted from 
Excel's 
Help, and comes across as jargon; needs more explanation, especially for 
non-US
people.

ISPMT
"amortized investment" is jargon, possibly not readily understood except 
in the
US. It gets no useful hits from Google.

ODDFYIELD
doesn't need to say "yield per 100 units" - yield is irrespective of 
this. 

XNPV
Excel documentation gives the formula. It's based on 365 days only. 
They've 
missed out a minus sign. More detail is required to define this 
function. 
Excel's help also seems to have an error - I don't think it is 
*necessary* to 
have a negative entry - first entry could be a payment. The day count 
appears 
to be the actual day count (366 in a leap year).

FTEST
"Summary: Returns the result of an F test (the probability that two 
datasets 
have come from the same total population)" 
Excel says it tests the probability that the *variances* are not 
significantly 
different (which is not the same as coming from the same total 
population).
"An F-test returns the one-tailed probability"
Excel currently describes this as the 2-tailed probability. I believe 
that is 
correct (see http://www.coventry.ac.uk/ec/~nhunt/pottel.pdf). Old 
versions of 
Excel eg 97 describe it as one tailed. It would be worth someone with 
real 
knowledge checking this out.

VDB
http://wiki.services.openoffice.org/wiki/Documentation/How_Tos/Calc:_VDB
_functio
n
has a rather more detailed explanation, and a link to (different) bugs 
in Calc 
and Excel.

Hope it's still helpful....


David King