<earlk@livenet.net>De: Earl Kiosterud 
Objet: Re: finding a point of intersection
Date : dimanche 14 novembre 1999 19:50

Salman;

I have a formula I wrote recently that does a linear interpolation to find
the intersect. The fellow for whom I wrote it then found an interpolation
add-in for Excel somewhere on the internet. It gives you three functions...
interpolationlinear(x,y,value), interpolationcubic(x,y,value) and
interpolationparabolic(x,y,value). I can sent it to you if you want.

For my linear interpolation formula:

The following will do a linear interpolation of the two data points above
and below your y value to draw the box you want. If your data points are
close together, the error will be small.

Your X and Y Values are in columns, and are named XRng and YRng
respectively. I used A2:A21 and B2:B21

set up the following:

C2: 0 (zero)
D2: your Y value
C3:=INDEX(Xrng,MATCH(D2,YRng))+((D2-INDEX(YRng,MATCH(D2,YRng)))/(INDEX(YRng,
MATCH(D2,YRng)+1)-INDEX(YRng,MATCH(D2,YRng))))*(INDEX(Xrng,MATCH(D2,B2:B21)+
1)-INDEX(Xrng,MATCH(D2,YRng)))
D3: =D2
C4: =C3
D4: 0 (zero)

set up a second series (Source data, Series).
X values: =C2:C4
Y values: =D2:D4
This requires an XY graph, which I assume you're using.

Regards,

Earl Kiosterud
earlk@livenet.net
-------------------------------------------------------------


Salman Ahmad wrote in message <382E5BA5.3B8DA4E4@mba2001.hbs.edu>...
>Is there a way (short of writing a macro) to find the point of
>intesection between two straight lines. Also can the method be used for
>intersection of two curves?
>
>Regards.
>
>Salman Ahmad
>