GNU set heatmap axis limits around a dynamically computed point - gnuplot

Question

I'm plotting a heatmap in gnuplot from a text file that is in matrix format:
z11 z12 z13
z21 z22 z23
z31 z32 z33
and so forth, using the following command (not including axis labelling, etc, for brevity):
plot '~/some_text_file.txt' matrix notitle with image
The matrix is quite large, in excess of 50 000 elements in the majority of cases, and it's mostly due to the size of my y-dimension (#rows). I would like to know if there's a way to change the limits in the y-dimension for a set number of values around a maximum, while keeping the x and z dimensions the same. E.g. if a maximum in the matrix is at [4000, 33], I want my y range to be centred at 4000 +- let's say 20% of length of the y-dimension.
Thanks.

Answer 1

Edit:
The solution below is basically the correct idea, however it works in my example but not in general because a bug in how gnuplot uses the stats command with matrix files. See the comments after the answer for further info.
You can do this using stats to get the indices that correspond to the maximum value dynamically.
Consider the following file which I named data:
0 1 2 3 4
0 1 2 3 4
0 1 2 3 4
0 1 5 3 4
0 1 2 3 4
If I run statsI get:
gnuplot> stats "data" matrix
* FILE:
Records: 25
Out of range: 0
Invalid: 0
Blank: 0
Data Blocks: 1
* MATRIX: [5 X 5]
Mean: 2.1200
Std Dev: 1.5315
Sum: 53.0000
Sum Sq.: 171.0000
Minimum: 0.0000 [ 0 0 ]
Maximum: 5.0000 [ 3 2 ]
COG: 2.9434 2.0566
The maximum value is in position [ 3 2 ] meaning row 3+1 and column 2+1 (in gnuplot the first row/column would be number 0). After running stats some variables are created automatically (help stats for more info), with STATS_index_max_x and STATS_index_max_y among them, which store the position of the maximum:
gnuplot> print STATS_index_max_x
3.0
gnuplot> print STATS_index_max_y
2.0
Which you can use to automatically set the ranges. Now, because STATS_index_max_x actually gives you the y (instead of x) position, you'll need to be careful. The total number of rows to obtain the range can be obtained with a system call (there might be a better built-in function, which I do not know):
gnuplot> range = system("awk 'END{print NR}' data")
gnuplot> print range
5
So basically you'll do:
stats "data" matrix
range = system("awk 'END{print NR}' data")
range_center = STATS_index_max_x
d = 0.2 * range
set yrange [range_center - d : range_center + d]
which will center the yrange at the position of your maximum value and will stretch it by +-20% of its total range.
The result of plot "data" matrix w image is now
instead of