From: Karl_Thompson@tigerfund.com
Date: Fri, 3 Jan 1997 07:47:13 -0500
Subject: Delphi Bug List
To: r.p.sterkenburg@dataweb.nl
Cc: 72366.306@compuserve.com

First, I would like to say that you are really doing a fine job 
editing the Delphi bug lists. I'm sure that your efforts are really 
appreciated. 

RE: Delphi 2.01

I noticed that one of the bugs you report is that the 
InternalRateOfReturn fuction in the Math unit calculates wrong 
answers. This does not appear to be the only function in the unit that 
has a problem. In fact, I can't find ANY financial function that works 
correctly. (Maybe you've already reported this.)

If finished testing the following functions in addition to the 
InternalRateOfReturn (I've checked the results against Excel, but they 
seem to be so obvious, I don't know how the unit made it out of 
Borland like it is.):

Z := NetPresentValue( 0.10, [1000], ptEndOfPeriod );

The result of the above should be 909.09. The function actually 
returns 1,000. After all, if an investment is made at the end of one 
period and the discount rate is 10% then the present value of the 
future amount must be less then the payment amount. 909.09 is the 
correct answer because if you work the formula in reverse, that is add 
10% to the number, you are back at 1,000. That is, invest 909.09 today 
and at the end of the first period, it will be worth 1,000. NOTE: if 
you pass the function the array [0, 1000] the result of 909.09 is 
returned.

Z := DoubleDecliningBalance( 10000, 0,  5, 1 );

The function returns 0.40 while the correct result is 4,000.00. Note 
that the depreciation for the second period is correct @2,400.00, but 
it is wrong again for periods 3 through 5. The correct answer of 
4,000.00 can be easily calculated. The value (10,000) divided by the 
Life (5) equals 2,000, double that equals 4,000 depreciation for the 
first year.

Z := FutureValue( 0.10, 1, 000, 100, {ptStartOfPeriod} ptEndOfPeriod );

First, this function returns a negative value. (I would hate to invest 
money at a positive rate and owe more money at the end of the period 
<g>.) 

In this example, the function returns -110.00. Actually, the answer 
should be $100. If the period of investment is for one period, and the 
investment is made at the end of that period, then no interest is due. 
When the TPaymentTime parameter is set to ptStartOfPeriod, the correct 
amount of interest is accrued (10.00) but as I mentioned, a negative 
value is returned. Actually, the results do not appear to change 
whether the last parameter is set to ptStartOfPeriod or ptEndOfPeriod.

I've not reviewed the code in the math unit, but it would appear that 
maybe there is a bug in a function that is being shared by these 
functions.

Karl


I'm sending along a PKZIP file of the sample project that I used to 
test these functions. You should recieve that as the next file. 
MATHBUGS.ZIP

Also, the CC: e-mail address is a compuserve account. If you need to 
contact me, would you mind sending your e-mail to both addresses?