How to use the function from a trend line?

[sremick]

So I have a chart that is plotting data in a series that is constantly being added to. It’s also plotting an exponential trend line projecting into the future. I have it displaying the trend line formula, but you cannot copy the formula or automatically utilize it in any way.

As the data series is regularly growing, the trend line formula is constantly evolving.

I would like to be able to do math automatically using this formula. Specifically, I want to determine the value for the X access for a given Y value. So this also means I need to invert the trend formula, which by default is the opposite of what I need (defaults to calculating Y for X).

As far as I can tell, not only can you not automatically use the trend line formula for anything actually useful, but you can’t even copy & paste the thing. I found one other person complaining about this, but there was no real solution (even though it was closed):

How to get the equation of a trend line in Calc?

Suppose I have a (xy scatter) diagram in localc and insert a trend line, for example a linear one of the type f(x) = ax + b. I know hot to display the equation in the diagram, but how can I reference to the parameters a and b in a cell to make further calculations with it?

Is there any hope to accomplish what I need? Why is this functionality (actually doing something useful with the trend line formula) missing?

[anon73440385]

Why is this functionality (actually doing something useful with the trend line formula) missing?

That’s not fully true. There are three functions: LINEST() (for polynomial trend lines), SLOPE() and INTERCEPT() (linear trend lines), though this doesn’t help in your case of exponential trend line.

Workaround:

1. Copy the formula object into an empty Draw document
2. Right click -> Break
3. Double click on the text (the text gets selected and you can copy the text using the usual methods)

> Is there any hope to accomplish what I need?

Almost nothing is without hope, but someone needs to write the required program code and developer resources willing to perform that on a volunteering bases are (obviously) rare.

[Lupp]

The trendlines in charts are calculated (afaik) by the regression functions also available in Calc sheets:
LINEST() and
LOGEST() .
Concerning the usage of LOGEST for exponential regression/approximation you find an example in the attachment. The mathematics -as far as needed to convert the representation of a regression function- is also explained a bit there.
ask288532exponentialTrendLineAndLogestFunction.ods

It might be useful to have a way to get the trendline equation(s) from the chart object, but I don’t know one.