Use of iteration function

[Eddy VG]

A mathematical formulae of the type A = E4*(1+(C4*E4)) in which C4 is
fixed value and A has values listed in a row in an excel-worksheet.
The different values of E4 has to be determined as a function of A.
Is there a iteration function available and how should it b
specified.
All advice is appreciated

 

[MrShorty]

Not quite sure what you are after and how iteration is necessary to
obtaining the solution.

Clarification: So you know A and C4 and you are trying to solve for
E4?

Assuming this is the problem:

Solution 1: Solver can do this, but it can be tedious running solver
manually when you have several equations to solve. Depending on your
math skills, this might be the easiest to implement in spite of its
tediousness.

Solution 2: Algebraically manipulate the equation into something of
the form 0=a*E4^2+b*E4+c, then use the quadratic equation to solve
[-b+/-sqrt(b^2-4ac)]/2/a.

Solution 3: Set up an set of iterative functions using the
Newton-Raphson's method (or other numerical root finding technique)
that will find the roots of the equation in solution 2. You would need
to turn iteration on (Tool - Options - calculation tab). This is the
same way that Solver works, only you can get it set up and not have to
call the Solver dialog each time you want a new solution.

Any way you try to do it, recognize that there will be two possible
solutions, they aren't always unique, and they aren't always real (and
Excel doesn't inherently know how to handle complex numbers).

 

[JE McGimpsey]

I'm not sure why you need an iterative function. A little algebra gives

C4*E4^2 + E4 - A = 0

E4 = (-1 ± SQRT(1^2 - 4*C4*(-A)) ) / (2*C4)

So one solution for E4 will be

E4 = (-1 + SQRT(1+4*$C$4*A))/(2*$C$4)

and the other will be

E4 = (-1 - SQRT(1+4*$C$4*A))/(2*$C$4)