Solving the TVM equation for the interest rate

[Dieter]

(04-15-2018 05:30 PM)Carsen Wrote:  If you solve for i, the answer is 2.152976E-11, rather than 0 when you leave the value of i at 0. This proves that since we changed the initial value in i from 0 to 0.001, it changed the result. It's almost like it uses the value in the i register as a initial guess. Just as you concluded before.

I can't say which of the previous values influences the new result, but at least one of them seems to do so.

(04-15-2018 05:30 PM)Carsen Wrote:  The Prime had to chime in because without a proper initial guess, the 50g would take minutes to solve for i.

There always is some kind of initial guess - the solver has to start somewhere. But if you don't give one and/or the solver does not set one on its own, the results can be random.

(04-15-2018 05:30 PM)Carsen Wrote:  To answer your first question, I think the 1/n estimate would be fine. Every time I used the equation to solve for i on my 50g and Prime solver, the initial guess of 1/n worked FANTASTIC. I was able to solve for i in seconds on my 50g with that initial estimate of 1/n.
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I also tried Angel Martin's initial guess equation on my 50g and Prime and it works too. I just had to divide it by 100 to get the percentage as a decimal.

I now have written an experimental version for the 11C / 15C and added this to the thread started by Gamo. The initial guess is calculated in a way I derived some time ago, cf. the formula at the end of this post. Could you also try this one and report the results?

Dieter