#### Curve-fitting

```I have a graph that I'd like to fit a curve to, but the 'trend-line'
function doesn't seem to get close.

Does anyone know of a spreadsheet that'll calculate a curve equation
from a given set of data?
--
Paul Hyett, Cheltenham (change 'invalid83261' to 'blueyonder' to email me)
```
 0
vidcapper (121)
3/14/2009 8:03:34 AM
excel 39879 articles. 2 followers.

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```Start here:

--
Gary''s Student - gsnu2007L

"Paul Hyett" wrote:

> I have a graph that I'd like to fit a curve to, but the 'trend-line'
> function doesn't seem to get close.
>
> Does anyone know of a spreadsheet that'll calculate a curve equation
> from a given set of data?
> --
> Paul Hyett, Cheltenham (change 'invalid83261' to 'blueyonder' to email me)
>
```
 0
GarysStudent (1572)
3/14/2009 10:14:01 AM
```On Sat, 14 Mar 2009 at 03:14:01, Gary''s Student
<GarysStudent@discussions.microsoft.com> wrote in microsoft.public.excel
:

>Start here:
>
>
Thanks. I'll have a look at Log, Power & Exponential - though in the
past none have provided that close a fit to my data.
--
Paul Hyett, Cheltenham (change 'invalid83261' to 'blueyonder' to email me)
```
 0
vidcapper (121)
3/14/2009 5:33:50 PM
```Paul Hyett  -

Your question is much too general.

For your specific situation, you are more likely to get an appropriate reply
if you (a) provide the data, (b) describe the pattern of the "average
relationship," and/or (c) explain the underlying physical phenomenon that is
being modeled.

If the trendline forms are not appropriate for your data, there are other
functional forms that can be fitted using Solver to search for the parameter
values.

-  Mike

http://www.MikeMiddleton.com

"Paul Hyett" <vidcapper@invalid83261.co.uk> wrote in message
news:QixNCVHHQ2uJFwP9@blueyonder.co.uk...
>I have a graph that I'd like to fit a curve to, but the 'trend-line'
>function doesn't seem to get close.
>
> Does anyone know of a spreadsheet that'll calculate a curve equation from
> a given set of data?
> --
> Paul Hyett, Cheltenham (change 'invalid83261' to 'blueyonder' to email me)

```
 0
mike5208 (300)
3/14/2009 6:33:51 PM
```On Sat, 14 Mar 2009 at 11:33:51, Mike Middleton <mike@mikemiddleton.com>
wrote in microsoft.public.excel :

>Paul Hyett  -
>
>Your question is much too general.
>
>For your specific situation, you are more likely to get an appropriate reply
>if you (a) provide the data, (b) describe the pattern of the "average
>relationship," and/or (c) explain the underlying physical phenomenon that is
>being modeled.
>
>If the trendline forms are not appropriate for your data, there are other
>functional forms that can be fitted using Solver to search for the parameter
>values.

Solver - now why didn't I think of that?

Thanks!
--
Paul Hyett, Cheltenham (change 'invalid83261' to 'blueyonder' to email me)
```
 0
vidcapper (121)
3/15/2009 7:17:37 AM
```Try the "smoothed-line" charting option - this looks like the shape a
flexible strip passing through your points could take up. A link to the basic
formula is here:
http://www.mvps.org/directx/articles/catmull/

If you have data in A2:B10 and an x-value in E2, enter this formula for the
y-value:

=SUM((1+1/IRR(MMULT({0,0,2,0;0,1,0,-1;-1,4,-5,2;1,-3,3,-1},
OFFSET(\$A\$2:\$A\$10,MATCH(E2,\$A\$2:\$A\$10)-2,0,4,1)-E2
)))^-{0;1;2;3}*MMULT({0,2,0,0;-1,0,1,0;2,-5,4,-1;-1,3,-3,1},
OFFSET(\$B\$2:\$B\$10,MATCH(E2,\$A\$2:\$A\$10)-2,0,4,1)))/2

To get values in the first and last data intervals, extend your data range
by one row at each end - you can do this simply by selecting A2:B3 and
dragging the fill handle up to row 1 and also selecting A9:B10 and dragging
down to row 11.

(Adjust the ranges to suit your data and fill down for more data values.)

"Paul Hyett" wrote:

> I have a graph that I'd like to fit a curve to, but the 'trend-line'
> function doesn't seem to get close.
>
> Does anyone know of a spreadsheet that'll calculate a curve equation
> from a given set of data?
> --
> Paul Hyett, Cheltenham (change 'invalid83261' to 'blueyonder' to email me)
>
```
 0
LoriMiller (18)
3/16/2009 12:59:01 AM
```On Sun, 15 Mar 2009 at 17:59:01, Lori Miller
<LoriMiller@discussions.microsoft.com> wrote in microsoft.public.excel :

>Try the "smoothed-line" charting option - this looks like the shape a
>flexible strip passing through your points could take up. A link to the basic
>formula is here:
>http://www.mvps.org/directx/articles/catmull/
>
>If you have data in A2:B10 and an x-value in E2, enter this formula for the
>y-value:
>
>=SUM((1+1/IRR(MMULT({0,0,2,0;0,1,0,-1;-1,4,-5,2;1,-3,3,-1},
>OFFSET(\$A\$2:\$A\$10,MATCH(E2,\$A\$2:\$A\$10)-2,0,4,1)-E2
>)))^-{0;1;2;3}*MMULT({0,2,0,0;-1,0,1,0;2,-5,4,-1;-1,3,-3,1},
>OFFSET(\$B\$2:\$B\$10,MATCH(E2,\$A\$2:\$A\$10)-2,0,4,1)))/2

Wow, that's quite a formula. :)
>
>To get values in the first and last data intervals, extend your data range
>by one row at each end - you can do this simply by selecting A2:B3 and
>dragging the fill handle up to row 1 and also selecting A9:B10 and dragging
>down to row 11.
>
>(Adjust the ranges to suit your data and fill down for more data values.)

I'll experiment - thanks.
--
Paul Hyett, Cheltenham (change 'invalid83261' to 'blueyonder' to email me)
```
 0
vidcapper (121)
3/16/2009 7:49:53 AM

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