gnuplot-info

[Gnuplot-info] Both positive and negative log y axis in same plot

[somesh <som...@gm...>]

Hi,

I have a data file like this:
#x  y
1   34
2   450
3   -987
4   20045
5   -1003
6   -30

For only positive values, just "logscale y" is fine. 
For only negative values, I can use a reversed logscale:
--
set logscale y
set yrange [ymin:ymax] reverse
plot file  u 1:(-$2) axis x1y1 t "Y" w linespoints
--

But how do I plot both positive and negative values in same plot? 
I want to place the x axis at the center of y axis; positive log scale (for
positive values) above the x axis, and reversed logscale (for negative
values) below the x axis.

Is it possible?

Thanks,
Somesh



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Re: [Gnuplot-info] Both positive and negative log y axis in same plot

[<l_b...@us...>]

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   Date: Thu, 24 Jan 2013 07:46:43 -0800
   From: somesh <som...@gm...>
   Content-Type: text/plain; charset="us-ascii"

   Hi,

   I have a data file like this:
   #x  y
   1   34
   2   450
   3   -987
   4   20045
   5   -1003
   6   -30

   For only positive values, just "logscale y" is fine. 
   For only negative values, I can use a reversed logscale:
   --
   set logscale y
   set yrange [ymin:ymax] reverse
   plot file  u 1:(-$2) axis x1y1 t "Y" w linespoints
   --

   But how do I plot both positive and negative values in same plot? 
   I want to place the x axis at the center of y axis; positive log scale (for
   positive values) above the x axis, and reversed logscale (for negative
   values) below the x axis.

How about

f(x) = (x >= 0 ? x : 1/abs(x));

plot file using 1:(f($2)) ....


Leo

Re: [Gnuplot-info] Both positive and negative log y axis in same plot

[BBands <bb...@gm...>]

That sort of approach is often useful in plotting certain types of
technical analysis indicators. One way I have seen that done is to
pick a pair arbitrary cutoff points near zero. You could try Googling
for John McGinley. He wrote on the subject back in the 1980s. His
solution was to plot a small slice of the chart just above and below
zero with a linear scale. I add a hatch to the region to make the
discontinuity clear. I haven't tried this in gnuplot, but Ethan
Merritt demoed some tricks using the ternary operator that should make
it doable.

    John Bollinger

On Thu, Jan 24, 2013 at 7:46 AM, somesh <som...@gm...> wrote:
> Hi,
>
> I have a data file like this:
> #x  y
> 1   34
> 2   450
> 3   -987
> 4   20045
> 5   -1003
> 6   -30
>
> For only positive values, just "logscale y" is fine.
> For only negative values, I can use a reversed logscale:
> --
> set logscale y
> set yrange [ymin:ymax] reverse
> plot file  u 1:(-$2) axis x1y1 t "Y" w linespoints
> --
>
> But how do I plot both positive and negative values in same plot?
> I want to place the x axis at the center of y axis; positive log scale (for
> positive values) above the x axis, and reversed logscale (for negative
> values) below the x axis.
>
> Is it possible?
>
> Thanks,
> Somesh
>
>
>
> --
> View this message in context: http://gnuplot.10905.n7.nabble.com/Both-positive-and-negative-log-y-axis-in-same-plot-tp17082.html
> Sent from the Gnuplot - User mailing list archive at Nabble.com.
>
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-- 
John Bollinger
www.BollingerBands.com

Re: [Gnuplot-info] Both positive and negative log y axis in same plot

[somesh <som...@gm...>]

Leo Butler wrote
> How about
> 
> f(x) = (x >= 0 ? x : 1/abs(x));
> 
> plot file using 1:(f($2)) ....
> 
> 
> Leo


BBands wrote
> That sort of approach is often useful in plotting certain types of
> technical analysis indicators. One way I have seen that done is to
> pick a pair arbitrary cutoff points near zero. You could try Googling
> for John McGinley. He wrote on the subject back in the 1980s. His
> solution was to plot a small slice of the chart just above and below
> zero with a linear scale. I add a hatch to the region to make the
> discontinuity clear. I haven't tried this in gnuplot, but Ethan
> Merritt demoed some tricks using the ternary operator that should make
> it doable.
> 
>     John Bollinger

Thanks Leo and John for the ideas!

I could do something similar to what I wanted by this:

f(x) = (x >= 0 ? log10(x) : log10(1/abs(x)));

then combine the following two plots (in linear scale) using multiplot ...
set yrange [0:4]
plot file using 1:(f($2)) 

set yrange [-4:0]
plot file using 1:(f($2)) 

The use of multiplot is to place two plots above and below the zero line.
Positioning is tricky but doable!

Thanks,
Somesh



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