gnuplot-info

[Gnuplot-info] map view of data matrix with block structure

[Michael L. <M_L...@ho...>]

Hello,

I'm making an image plot ('set view map') of a 27x27 correlation
matrix that has a block diagonal structure. The [1:18,1:18] 
top-left submatrix and the [19:27,19:27] lower-right submatrix are
all positive and closer to +1; the off-diagonal submatricies 
are all negative and closer to -1.  My problem is that on
the boundary gnuplot is interpolating and plotting a 
color that indicates it is near zero. What I want is 
a sharp distinction between the boundaries but nice
color gradients in each submatrix showing the transition
towards +/- 1.  Any help would be much appreciated.

Here's what I've done so far
---
set pm3d
set view map
set size square
set palette model RGB
set noxtics
set noytics

set palette defined (my nice blue to red pallette choice)

splot "cormatrix" matrix with pm3d # for example

set xrange [] reverse
set yrange [] reverse
replot
---

Thanks,
Mike

Re: [Gnuplot-info] map view of data matrix with block structure

[Hans-Bernhard B. <br...@ph...>]

Michael Lasarev wrote:
> are all negative and closer to -1.  My problem is that on
> the boundary gnuplot is interpolating and plotting a 
> color that indicates it is near zero. 

Re-read "help set pm3d", in particular all the mentions of the 
"corners2color" option.

> What I want is a sharp distinction between the boundaries but nice 
> color gradients in each submatrix showing the transition towards +/-
> 1.

That wish is quite self-contradictive.

You may want to re-map the z value to conserve dynamic range neare +/-1,
while wasting as little space as possible on the intervening region. 
Something like

	splot 'file' u 1:2:(tanh(0.95*$3))

maybe.

[Gnuplot-info] Re: map view of data matrix with block structure

[Michael L. <M_L...@ho...>]

Hans-Bernhard Broeker <broeker <at> physik.rwth-aachen.de> writes:

> 
> Michael Lasarev wrote:
> > -snip-
> > What I want is a sharp distinction between the boundaries but nice 
> > color gradients in each submatrix showing the transition towards +/-
> > 1.
> 
> That wish is quite self-contradictive.
> 
 I wrote that poorly, you're right. I meant that I wanted
 a clear distinction between the positive- and negative-valued
 blocks of the matrix but with a gradient within each
 positive (negative) block showing how the values transition
 towards +1 (-1). [They are already close to the boundaries with
 absolute values > 0.8, mostly.] For instance a blue gradient 
 within the positive-valued block and a red gradient in the 
 negative-valued block, but without a 'zero colored' margin where
 it transitions from -0.8 to +0.8.

 corners2color did help, thank you. I also had good results
 by converting the matrix into three separate columns (x-position,
 y-position, z-position=correlation) and then 
   splot 'three_cols_of_data' u 1:2:3:3 with points pt 9 ps 0.70 palette
 
--Mike