forum.vdsworld.com

Mac · Posted: Thu Jan 16, 2003 4:03 pm Post subject:

I think you'll have to use an incremental rate (starting at .001 or so,
and incremented by .001), and test it each increment to see if it's
correct to make all months come out as they should - if so, there's
gonna be a whole lotta loopin' going on. Wink

BTW, I'd still like to know how ya worked out 10 to the power of 1/12... Wink

Cheers, Mac Smile

arcray · Posted: Thu Jan 16, 2003 5:40 pm Post subject:

Sorry for the non responsiveness. I have been very busy.

I did use the '^' as an indicator of raising to the power of.

%Y can be equal to 12 as the payment is always monthly in this case. In cases it could be daily 1/365th!, but not here.

So:-

jwfv · Posted: Thu Jan 16, 2003 7:06 pm Post subject: Figuring APR

I dealt with the APR problem several years ago in a Clipper application. I can tell you that the only way I found to figure it out is a loop that increments a "test" apr by small amounts until it works out. The math guys I talked to called it a "non-linear" equation.

If anyone is interested, I can post the Clipper code. It is not very complicated, and should be able to be duplicated in VDS, if you are familiar with basic Clipper/dBase programming terminology.

Smile

vdsalchemist · Posted: Thu Jan 16, 2003 7:11 pm Post subject:

Hi jwfv,
Yes please post your clipper code:)

Andy,
That is the direction I was going in myself. You should be able to use Logs to figure this out... I am looking for a calculation that uses Logs...

jwfv · Posted: Thu Jan 16, 2003 7:22 pm Post subject: Clipper code - Figuring APR

This is what I have used for many years in issuing loans.

This function accepts 3 variables:

nAmtFin - the amount to be loaned out

nPayment - the amount of each payment (simply the TOTAL that will be paid including interest/fees, divided by the numer of payments)

nNumPmts - the number of payments

With these 3 values, it begins testing APRs and increments or decrements it until it gets to the answer.

Hope this helps. Here is the code:

FUNCTION joeAPR(nAmtFin, nPayment, nNumPmts)
LOCAL nTestAPR := 1.00, nMonthRate, nTestAmtFin, nAdder :=50.00, nCtr := 0, diff := 0
LOCAL JOEVAR:=.F.
DO WHILE JoeVar=.F.
nTestAPR := nTestAPR+nAdder
IF ++nCtr>500
RETURN 999.99
ENDIF
nMonthRate := nTestAPR/100.0000/12
nTestAmtFin := nPayment*((1-(1+nMonthRate)^(-nNumPmts))/nMonthRate)
IF nTestAmtFin = nAmtFin
EXIT
ENDIF
IF nTestAmtFin<nAmtFin
IF nAdder=50
nAdder := 25
nTestAPR := nTestAPR-50
LOOP
ENDIF
IF nAdder=25
nAdder := 10
nTestAPR := nTestAPR-25
LOOP
ENDIF
IF nAdder=10
nAdder := 5
nTestAPR := nTestAPR-10
LOOP
ENDIF
IF nAdder=5
nAdder := 2.5
nTestAPR := nTestAPR-5
LOOP
ENDIF
IF nAdder=2.5
nAdder := .5
nTestAPR := nTestAPR-2.5
LOOP
ENDIF
IF nAdder=.5
nAdder := .01
nTestAPR := nTestAPR-.5
LOOP
ENDIF
EXIT
ENDIF
LOOP
STORE .T. TO JoeVar
END DO
IF nTestAPR-nAdder>999.99
RETURN 999.99
Else
RETURN nTestAPR-nAdder
Endif

Serge · Posted: Fri Jan 17, 2003 10:11 am Post subject:

i have done some investigating, ray, and i can do the apr thing for you using logs in vds BUT i need to know exactly what formulae to use

the web site you suggested is contradictory and makes no sense to me eg. at one stage, he says that P is the annual interest rate and then he says that P is the APR!?!!?!

i looked at the example you posted and some things were not clear:

- how do you work out what you need to pay each month?

- i noticed that the interest rate decreases each month, how do you work out the interest rate for each month?

- and so on...

i need to know exaclty what formulae you used to work out each value in the table you put together for us even if you give me the formulae used by excel at each stage

arcray · Posted: Fri Jan 17, 2003 1:14 pm Post subject:

Serge

I don't have all the info with me at the moment, but will put it all together over the next couple of days for posting here.

Cheers

jwfv · Posted: Fri Jan 17, 2003 2:09 pm Post subject: APR

I will be interested to see if someone comes up with a formula for figuring this out. I was always told that there is no formula for it. The answer I got is that if you have a term loan with equal payment amounts and you are charging a pre-figured amount of interest (not pre-figured interest RATE, but a pre-figured dollar amount of interest), that you could not figure the A.P.R. linearly, but had to estimate, calculate, adjust, recalculate, etc. ... until you reached the answer.

By the way, as you can see in my Clipper solution above, the actual code is very simple. Most of it is simply changing the "adjustment amount" to try to arrive at the answer more quickly. When this code was written, the fastest processor out was the new 286! It was like a supercomputer.

jwfv · Posted: Thu Sep 29, 2005 7:24 pm Post subject:

Reviving an old post, because I have a need to implement this function in VDS.

Is there a way to do exponents in VDS? 2^3 or 2^(-1), etc.?

Serge · Posted: Fri Sep 30, 2005 2:14 am Post subject:

vdsalchemist · Posted: Fri Mar 24, 2006 8:16 pm Post subject:

Hi All,
I was thinking the other day how to do these things with just plain VDS instead of using a DLL. I have finally found a solution that works for most cases. See the code below.

jwfv · Posted: Fri Mar 24, 2006 8:21 pm Post subject:

Looks pretty cool! I'll try to digest it over the weekend.

vdsalchemist · Posted: Fri Mar 24, 2006 11:45 pm Post subject:

BTW the fraction 1/12 can also be converted to a floating point using the @fpow() like below.