TI-83 irr function gives errors...


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TI-83 irr function gives errors...



just try the following
 Using the following calculation:
       irr(-100,{150,200,-100}) gives 120.20
 but :
       irr(-100,{150,200,-101}) results in -58.75
 and controlling the npv function, we have :
       npv(120,-100,{150,200,-101}) results in 0.02
       npv(120.035,-100,{150,200,-101}) results in -6.8173E-4
 that is the I% value for whitch nvp(I%,...) results in 0 is something
 between
   120 and 120.035 ...


Following : the mails exchanged with TI support services !!

Suj :  Re: Guarantee
Date : 13/11/98 22:49:31
From: cpalomino@ti.com
Reply-to: ti-cares@ti.com
To: JmChe7@aol.com

Jean-Marie,

Thank you for your reply.

We are still researching this TI-83 function, unfortunately we do not make
any payment / reimbursement guarantees to our calculator users. (as in this
case) I will send another message to my calculator specialist asking for
more information concerning this IRR function.

Regards,
Chris


========================= ORIGINAL MESSAGE ==========================

[ JmChe7@aol.com on 11/9/98 3:41:38 AM ]

Dear Christopher Palomino
I am still waiting for Guarantee about my TI-83 calculator...(repayement
!!)
and i find your answer takes quite a long time about this subject.
Must I understand I need to follow a more procedural way to obtain redress
or
compensation for.. ??!!
Best regards
Jean-Marie Chevalier
========================= PREVIOUS MESSAGES... ==========================
Suj :      Re : Re: Incorrect result with TI-83 financial function irr...
Date :    28/10/98 22:47:55
From:     cpalomino@ti.com
Reply-to: ti-cares@ti.com
To:  JmChe7@aol.com
Thank you for your reply.
Good point Jean-Marie. Much like the payment algorithims used in our
financial calculators, these calculators accept a positive payment although
this money is going OUT of your pocket. I will forward your comments to my
senior technical analyst.
If you have any questions please feel free to contact us. Please copy this
message in your response and mail to:    ti-cares@ti.com
Best Regards,
Chris
========================= ORIGINAL MESSAGE ==========================
[ JmChe7@aol.com on 10/27/98 5:22:25 AM ]
Christopher (Palomino)
Thanks for your reply... I just have a new idea (solution) to resolve the
problem encountered  (if it can help you) :
The calculation for the resolution of "npv(I%,...) = 0 " must be done with
I%
values ranging from positive I% values downto negative I% values in order
to
return the correct I% value.
(sometimes, a negative result is correct in the sense the payment terms
correspond to a loss in money, resulting in a negative I% ratio)
I think you are doing this from negative to positive I% values, and so the
result in not the one attempted, because this equation has sometimes 2
solutions : a positive AND an a negative I% value (depending on the
ponderation of each term of the payment series)
best regards,
Jean-Marie Chevalier
======== Previous mails ==============>>
<< Suj :   Re: Incorrect result with TI-83 financial function irr...
 Date :   26/10/98 18:29:34
 From:    cpalomino@ti.com
 Reply-to:     ti-cares@ti.com
 To: JmChe7@aol.com
 Jean-Marie,
 Thank you for your recent e-mail. We appreciate your support of our
 products.
 I'm going to forward your message to a calculator specialist and ask for
 more information concerning this internal algorithm. I will let you know
 the result of our conversation in a follow-up e-mail.
 If you have any further questions or comments please feel free to contact
 us at your convenience. Please copy this message in your response and send
 directly to ti-cares@ti.com for faster service on replies.
 Best Regards,
 Christopher Palomino
 ------------------------------------------------------------------------
 Educational & Productivity Solutions
 Customer Support Center                E-mail: ti-cares@ti.com
 Texas Instruments
 PO Box 650311 M/S 3962
 Dallas, TX  75265                      (972)917-8324 (Technical Help)
                                        (800) 842-2737 (General Info)
 ------------------------------------------------------------------------
  www.ti.com/calc
 ========================= ORIGINAL MESSAGE ==========================
 [ JmChe7@aol.com on 10/19/98 4:26:10 AM ]
 From a financial (and not mathematical) point of view, a rate is a
positive
 value.
 Using the following calculation:
       irr(-100,{150,200,-100}) gives 120.20
 but :
       irr(-100,{150,200,-101}) results in -58.75
 and controlling the npv function, we have :
       npv(120,-100,{150,200,-101}) results in 0.02
       npv(120.035,-100,{150,200,-101}) results in -6.8173E-4
 that is the I% value for whitch nvp(I%,...) results in 0 is something
 between
   120 and 120.035 ...
 in the TI-83 annexes, we found : irr returns I% for  nvp(I%,...) = 0
 the equation resolution for "  nvp(I%,...) = 0 " doesn't respect the basic
 rules that I% must be a positive value !!
 Concerning the Guaranti for this TI-83 calculator, what can I expect from
 TI
 ??
 best regards
 Jean-Marie CHEVALIER
  >>