Graham -
You could access the trendline formula using the LINEST worksheet
formula. Bernard Liengme shows how to do this for a polynomial fit,
which should help you figure it out for another fitted model:
http://www.stfx.ca/people/bliengme/E...Polynomial.htm
Or you could extract it directly from the trendline formula using Dave
Braden's parsing macro:
http://www.google.co.uk/groups?selm=....microsoft.com
Now put some X values in a column at the frequency you want, and use the
coefficients you've determined to calculate the corresponding Y values
in the next column, and put your own custom trendline on the chart.
- Jon
-------
Jon Peltier, Microsoft Excel MVP
Peltier Technical Services
Tutorials and Custom Solutions
http://PeltierTech.com/
_______
Graham Wideman wrote:
Partially answer!
Well, at least a better diagnosis:
Turns out that the symptom noted (dashed lines on trendlines print as
continuous lines) only occurs for curved trendlines (such as polynomial),
not linear.
It appears that what's happening is this:
Excel is indeed using the dashed line format, applying it to the dashed
lines between the points that it's calculating for the trendline.
But the higher the resolution of the picture (eg: printing, or zooming in)
the more finely does Excel calculate the points, And hence the shorter those
line segments... to the point where the the length between the points is
less than the length of even one dash.
Hence the appearance of a continuous line, albeit a bit messy in some views
as the adjacent initial dash segments somewhat jumble together.
OK, so this could be relieved if one could set the interval at which Excel
calculates the curve, but I don's see such a setting in the UI or a property
in the object model.
Alternatively, with some programming, if one had access to the trendline's
data series, one could set a pattern of alternating line-segment colors (or
say 3 white, 3 black, 3 white... if they are very fine). But I don't see a
way to get at the trendline's series either.
Any other ideas?
Graham