You have SLOPE, INTERCEPT and LINEST, making an interpolation is rather easy
from there.
best wishes
--
Bernard V Liengme
www.stfx.ca/people/bliengme
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"Dan Gauthier" <Dan wrote in message
...
Please add this function which may be used either for a vector set of data
or
for a 2 dimensional array of data.

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Bernard Liengme wrote...
You have SLOPE, INTERCEPT and LINEST, making an interpolation is rather easy
from there.
....

LINEST would be gross overkill. Besides, FORECAST and TREND would be
far easier than any of these. The problem is that using it to
interpolate in a table (TBL) for a value (v) involves expressions like

TREND(OFFSET(TBL,MATCH(v,INDEX(TBL,0,XvalCol)),Yva lCol-1,2,1),
OFFSET(TBL,MATCH(v,INDEX(TBL,0,XvalCol)),XvalCol-1,2,1),v)

You may like these, but they are a bit long. When they're general like
this, they eat 3 levels of nested function calls. A simpler approach
would be handy, but I suspect we won't see it in Excel until a few
months after Hell organizes an Ice Hockey league.

I would agree with the OP on this one. LINEST etc. are curve fitting
functions, not interpolating functions. Sometimes when you have a
table of data, it is easier/preferable to approximate the function as a
series of straight lines connecting the data points (similar to what a
line chart/XY chart does) rather than attempt to fit the data to a
curve.


--
MrShorty
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Which you can do with LINEST etc. or more directly with TREND or
FORECAST by including just the relevant surrounding points (instead of
the entire data set) for a given interpolation.

Jerry

MrShorty wrote:

I would agree with the OP on this one. LINEST etc. are curve fitting
functions, not interpolating functions. Sometimes when you have a
table of data, it is easier/preferable to approximate the function as a
series of straight lines connecting the data points (similar to what a
line chart/XY chart does) rather than attempt to fit the data to a
curve.

Correct you can use the built in functions for interpolation easily
enough, once you've located the interval containing the desired value.
And if you have a small dataset and/or only need to perform the
interpolation a few time, manually searching through the dataset for
the interval wouldn't be a problem. On the other hand, if you have a
large dataset or need to perform several interpolations, manually
searching for the interval and adjusting formulas accordingly gets
tedious. As Harlan points out, composing a formula to search for the
interval then interpolate is not a "pretty" formula. I wanted an
interpolate function when I converted to Excel from Quattro Pro (which
had a built in interpolation function), so I wrote a UDF, but it would
be nice if Microsoft would include it as a built in function.

Jerry W. Lewis Wrote:
Which you can do with LINEST etc. or more directly with TREND or
FORECAST by including just the relevant surrounding points (instead of
the entire data set) for a given interpolation.

Jerry

MrShorty wrote:

I would agree with the OP on this one. LINEST etc. are curve
fitting
functions, not interpolating functions. Sometimes when you have a
table of data, it is easier/preferable to approximate the function as
a
series of straight lines connecting the data points (similar to what
a
line chart/XY chart does) rather than attempt to fit the data to a
curve.


--
MrShorty
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