four-parameter logistic equation

Hello AJ,

Not sure what your are asking of Solver. Do you have a set of (x,y) data

that need to be fitted to the stated equation?

Possible worksheet starting in A1

top 1 (some starting guesses)

bottom 1

logEc 1

Hillslope 1

x y y(calc)

1 23 99

2 34 104

etc

Let the parameters be in B1:B4

Let the X's be in A10:A50, Y's in B10:B50 and Y(Calc) in C10:C50

The y(calc) values come from your formula

In another cell Say B5 enter this formula

DevSq = SUMXMY2(B10:B50, C10:C50)

Have Solver minimize the value in B5 by varying B1:B4

Now you should have a fairly good agreement between Y and Y(calc)

I would invite you to email me the file but I am off on vacation this

weekend.

Best wishes

Bernard

www.stfx.ca/people/bliengme

Quote:

> Hi

> I am having problems trying to get Excel to do a four-parameter

> logistic equation using the solver add-in.

> y=Bottom + ((Top - Bottom) / (1+ 10(logEC50-X).HillSlope))

> Can anyone tell me if I am asking too much of Excel.

> I have some values got from a curve fitting program (Prism) but when I

> pull them into my equation the curve is no where near the orginal raw

> data.

> Any suggestions will be useful

> Yours

> Aj

> Newport

> Fife