Logarithmic Trendline doesnt work !

[glikoz]

Do i miss the point of issue ?
I try to make logarithmic trendline example .
If you try to feature demo ,
go Welcome !\Functions\Extended\Trendline tab
select logarithmic from combobox ,
The trendline is drawn over the x axis , (It seems its values are "zero")
So is there any patch ?
Thx for advice ..

[Narcís]

Hi glikoz,

It works fine for me here using latest version available at the client area, which was posted last Friday. Which TeeChart version are you using?

Here the line is near zero but is not a constant line, it has a light slope.

[glikoz]

We have January 2007 release of TeeChart,
Already April Release does not include update about Logarithmic Trendline.
In Feature Demo Program you could easily recognize that Logarithmic Trendline produce only two points . Some times it has got tiny slope some times never (all points on zero base)..

Also we test Logarithmic TrendLine in Excel ..
It has got 27 points for 27 values..
But in Teechart , it has got only 2 points for 27 values ..

Please Check Again ,
you could see problem ..
We are waiting urgent response.Thx again.
Best regards..

[Narcís]

Hi glikoz,

We are investigating the issue. The first problem we can see is that with logarithmic trendline all x and y values need to be positive.

We will get back to you when we have more information.

Thanks for your patience.

[Narcís]

Hi glikoz,

As a follow up to this issue, this function type is not supported, but he can do it by :
a) linearizing fit equation.
b) using polynomial fitting on linearized equation
c) at the end, transform results back to original space.

For example, if you want to fit y=Exp(a*x), you say Exp(a*x) = X , calculate new Xs and then do normal line fit on: y = X.