(32S) Accurate TVM with direct solutions

[Jeff_Kearns]

(12-30-2015 12:13 PM)Dave Britten Wrote:  

(12-30-2015 08:22 AM)Dieter Wrote:  Dave's program returns the results immediately by direct calculation – no solver and no iterations required, and the user also does not have to provide two initial guesses.

Maybe the program even is a tiny bit more accurate since it seems to include implementations of both an e^x–1 and a ln(1+x) function, while the version you suggested only does the latter.

So both versions have their benefits. Yours is very short and compact while Dave's is faster and returns directly calculated results immediately.

Dieter

Right, this one is built for speed (which is often important when making quick financial decisions). As such, it makes quite a few sacrifices on size. I do have a one-label solver-based version kicking around for when I only need to run a few numbers, and don't want to type in a large program. Or better yet, I just grab my 17BII.

Gents ~

While I applaud Dave for including his 'direct solutions' program, I have to disagree with a number of statements you each made. First of all, the accuracy of the 38-line, single-label SOLVER program is on par with that of any financial calculator. It includes both functions (e^(x–1) and ln(1+x)) to which you refer. Just test it with the example in the 15C Advanced Function Handbook, repeated here, or with any other TVM problem.

"...and the user also does not have to provide two initial guesses": Believe it or not, this is not (or perhaps seldom) required with the solver program. It works just fine without ever providing initial guesses - except perhaps if one is trying to torture test the program with an extremely high 'N' or a very, very small 'I'.

"...Dave's program returns the results immediately": You mean after entering all the variables (unprompted), and looking up which of the routines to execute? If you find waiting a second or two for an answer to a TVM problem, 'on the fly', onerous, then I have no comment. FYI, when solving Dave's example, above - I get the same answer in less than one second.

"So both versions have their benefits...Dave's is faster and returns directly calculated results immediately": Dave's 13 label, 122 line program has no practical advantages whatsoever. It is not faster to use at all (especially when you have to set flags...), uses up almost all the available memory, and still requires the solver for interest rate calculations. The calculator has a SOLVER; it is meant to be used!

"...I do have a one-label solver-based version kicking around for when I only need to run a few numbers, and don't want to type in a large program": I think you should type in the 38-line program and test it. You will see that it meets all your TVM needs, especially speed and accuracy ;-).

Jeff