Re: [Gnuplot-info] log color bar: out of range data --> invisible

[theozh <th...@gm...>]

> Same way. http://gnuplot.sourceforge.net/docs_4.2/node333.html
>
> On Thu, Apr 2, 2015 at 2:19 AM, theozh <th...@gm...
> <mailto:th...@gm...>> wrote:
>
>     That's ok for column data...
>     But how do you do it with matrix data?

This works if you have your matrix data in column form:
x1 y1 z1
x2 y2 z2
x3 y2 z3
x4 y4 z4
...

But how do you do operation if you have it in matrix form?
z11 z12 z13 z14
z21 z22 z23 z24
z31 z32 z33 z34
z41 z42 z43 z44


To illustrate the strange observation

If you have a file "Matrix1.dat"
1	2	3	4
2	-3	4	5
3	4	-5	6
4	5	6	7

set palette rgbformulae 7,5,15
set logscale cb
plot "Matrix1.dat" matrix with image

The negative values will be displayed with the minimum color, i.e. black


However, if you have a file "Matrix2.dat"
1e-8	2e-8	3e-8	4e-8
2e-8	-3e-8	4e-8	5e-8
3e-8	4e-8	-5e-8	6e-8
4e-8	5e-8	6e-8	7e-8

set palette rgbformulae 7,5,15
set logscale cb
plot "Matrix1.dat" matrix with image

The negative values will be displayed with the maximum color, i.e. yellow.

What is the reasoning behind that?