Trendline equation

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Laurent BP Laurent BP
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Trendline equation

Hi,

In chart, you may add a trendline to almost all type of chart. However, the equation is significant only for XY scatter diagrams. I proposed to remove the equation (not the trendline, only the equation) of all type of chart, except for XY chart.
https://bugs.freedesktop.org/show_bug.cgi?id=74163

Do you know some case, where the user would require the equation of the trendline for other type of diagram different from XY scatter chart?
LibreOffice 5.3.5
Stefan Weigel Stefan Weigel
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Re: Trendline equation

Hi,

Am 30.01.2014 22:12, schrieb Laurent BP:

> https://bugs.freedesktop.org/show_bug.cgi?id=74163


> Lets take an example which corresponds to a common error of beginner:
> 1. Enter Data such as X=1, 10, 100 and Y=11, 12, 13
> 2. Create a *XY* (scatter) chart
> 3. Insert trendline and show equation
> => f(x) = 0.0165165165x + 11.3888888889
> With same data:
> 4. Create a *Line* chart with  "First column as label" selected on 2nd step
> 5. Insert linear trendline and show equation
> => f(x) = 1x + 10

> Do you know some case, where the user would require the equation of the
> trendline for other type of diagram different from XY scatter chart?

Yes, I do.

Example:

1. Enter Data A1=11, A2=13, A3=12, A4=14, A5=16, A6=15
2. Select A1:A6
3. 4. Create a Line chart
4. Insert linear trendline and show equation

--> Equation does make sense.

;-)

As long as you do *not* specify X-values or categories, the equation
is usefull even for "Column", "Bar", "Area", "Line" and "Column and
Line" charts.

Cheers,
Stefan


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Laurent BP Laurent BP
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Re: Trendline equation

Stefan Weigel wrote
1. Enter Data A1=11, A2=13, A3=12, A4=14, A5=16, A6=15
2. Select A1:A6
3. 4. Create a Line chart
4. Insert linear trendline and show equation

--> Equation does make sense.
If you do not specify X-values/categories, what sense can you give in the equation for 'x'?
From my point of view, equation is useful if you need to extrapolate or interpolate values. What else?
The trendline give you the trend of your data, but the numerical values of the equation must be linked to something. Did I mess something?
And what about "forced intercept" (new option for 4.2), which sense can user give for categories value of zero?
LibreOffice 5.3.5
Stefan Weigel Stefan Weigel
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Re: Trendline equation

Hi again,

Am 31.01.2014 12:35, schrieb Laurent BP:

> Stefan Weigel wrote
>> > 1. Enter Data A1=11, A2=13, A3=12, A4=14, A5=16, A6=15
>> > 2. Select A1:A6
>> > 3. 4. Create a Line chart
>> > 4. Insert linear trendline and show equation
>> >
>> > --> Equation does make sense.

> If you do not specify X-values/categories, what sense can you give in the
> equation for 'x'?
> From my point of view, equation is useful if you need to extrapolate or
> interpolate values. What else?

Sure.

A1= Oct | B1= 1100 US$
A2= Nov | B2= 1300 US$
A3= Dec | B3= 1200 US$
A4= Jan | B4= 1400 US$
A5= Feb | B5= 1600 US$
A6= Mar | B6= 1500 US$

Create a Column chart. Insert formula.
Formula reads: f(x) = 88,57x + 1040

You can use the formula displayed in a Line chart or Column chart in
order to extrapolate the row to the following months. X would be the
number of the month, counting from October = 1.

Extrapolate July: f(x=10) = 1926

No matter if you do specify X-values or categories or not. Anyway,
there are lots of cases, where the formula is usefull in a regular
chart that does not need to be a XY chart.

Stefan.


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Laurent BP Laurent BP
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Re: Trendline equation

Hi Stephan,

I have to agree with your example.

Another case in when X-categories are date instead of text.

Then I would propose to add a warning message about the limit of usability of such equation.
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Stefan Weigel Stefan Weigel
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Re: Trendline equation

Hi,

Am 03.02.2014 12:40, schrieb Laurent BP:

> I have to agree with your example.
>
> Another case in when X-categories are date instead of text.

Since a date basically is nothing else than a serial number, in many
cases dates should be usable for X-Values in a trendline equation as
well.

if you see 04. Feb 14 the cell value (x) is 41674
if you see 05. Feb 14 the cell value (x) is 41675
if you see 06. Feb 14 the cell value (x) is 41676
if you see 07. Feb 14 the cell value (x) is 41677
if you see 08. Feb 14 the cell value (x) is 41678

Stefan
:-)


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