GROWTH function falls over..

  • Thread starter Thread starter Phil C
  • Start date Start date
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Phil C

Hi All

I am using the GROWTH function to calculate the y-axis intercept (i.e. value
of y at x = 0) for an exponential function where I have four (x,y) values.
This works fine, but if the user goes back and deletes one of the input data
points (say if they decide it is a rogue point ...or just do it out of
mischief!) the function fails (returns #VALUE). I have a trendline based on
the extrapolated line which then also falls over. I get the same result if I
calculate the slope and intercept using LOGEST and then use the formula to
calculate y at x=0.

Any way around this? I would like to instruct program thus:

If an x or y value is deleted, re-calculate y-axis intercept based on the
remaining points.
And do this unless remaining number of data points in less than 2.

Many thanks

Phil
 
GROWTH(), LOGEST(), LINEST(), and TREND() do not permit missing values.
Slope and Intercept do permit missing values, so assuming that you
have only a single x-variable, then
=EXP(SLOPE(IF(ISNUMBER(ydata),LN(ydata)),xdata))
=EXP(INTERCEPT(IF(ISNUMBER(ydata),LN(ydata)),xdata))
will give you the LOGEST coefficients, while permitting missing data.

These formulas must be array entered (Ctrl-Shift-Enter)

Jerry
 
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