ja********@gmail.com wrote:

to**************@uniroma1.it wrote: It might not have solutions or have multiple (2) solution, depending on

A,B,C.

Thanks for your help, please let me know if you have any observations

about my adaptation.

Your function is like a lot of Access problems. I.e., different

conditions lend themselves to different solution techniques. Let's

look at the function.

f(x) = e ^ (Ax) - Ax - C

When x is very negative, f(x) looks similar to -Ax. When x is very

positive, f(x) looks like e ^ (Ax). The inflection point is when x =

0. The function is fairly flat near the inflection point. So f(x)

would be a somewhat reasonable way, for example, to approximate a

variable delay to an exponential function. The positive point where

f(x) = 0 can be thought of as the amount of time a delayed exponential

needs to break through a threshold. The minimum value of f(x) is 1 -

C, so C must be >= 1 for f(x) = 0 even to have a real solution. The

problem is that unless 1 - C is a reasonable distance below the x-axis,

the flat region has the potential to send p(k) off to places that even

Double will choke on. Once C is reasonably large, f(x) is so smooth

that convergence will happen quickly with almost any method. Note that

for this case the Newton-Raphson method will converge quite rapidly.

So I would check convergence for values of C slightly larger than one

with different values of A to see if Newton-Raphson is adequate for the

range of values you expect A to take.

James A. Fortune

CD********@FortuneJames.com