Plus42 Equations, Preview Release

[Albert Chan]

(06-08-2022 04:57 PM)Thomas Okken Wrote:  Hmm, it looks like the I%YR improvement wasn't such an improvement after all.
I'll look into it, it looks like 1.0.6 won't be far behind...

(Specifically, the revised starting guess doesn't work for PMT=0, but it doesn't actually make sense to use the iterative I%YR solver in that case. When PMT=0, I%YR can be calculated directly, without needing iteration at all.)

What do you mean ?

With PMT=0, nonzero (PV,FV), edge rates = PMT/FV, -PMT/PV, both 0%, perfectly valid guess rate.
Edge rate is not meant for close to true rate, only to guarantee convergence (if solution exist)

Example, n=36, PV=-10000, PMT=0, FV=20000

I = 0% --> 1.869% --> 1.944% --> 1.944%

---

There is indeed a flaw with I%YR solver. It *assumed* solution exist, without confirmation !

do_i_pct_yr() seach loop terminate if (f=0) or (f'=0) or (--count==0) or (new_i==i)
After termination, it just returned the last i, which may not be a solution.

Example: n=36, pv=-10000., pmt=500., fv=-9000

I%YR solver return 6.2488% ??? (without warning!)
Correct answer is no solution.