[Gnuplot-info] Troublesome warning message

[<she...@be...>]

Hi folks

I have written a gnuplot script (which appears below) that reads and plots
image data from an ascii file. The file contains multiple 2D images and the
script advances through the images depending upon whether an up or down
arrow key is pressed. Presently the script displays the images correctly
when the arrow keys are pressed but the script generates the following
warning repeatedly:

   warning: matrix contains missing or undefined values

This warning message appears to be slowing the display of the images
upon making the button press.

Does anybody have an idea why this warning is appearing?


reset
unset key
unset colorbox
unset border
unset xtics
unset ytics
unset ztics
set palette gray

set multiplot
i = 0
set size .25,1
set origin 0,0
set xrange [0:5]
set yrange [0:25]
plot 't_space.dat' index i using 1:2:3 with labels left
set autoscale
set size square 1
set origin .10, 0
plot 't_space.dat' index i+1 matrix with image
unset multiplot


# Advance or decrement the slice depending upon key press.

bind "Up" "i=i+2;              \
           reset;              \
           unset key;          \
           unset colorbox;     \
           unset border;       \
           unset xtics;        \
           unset ytics;        \
           unset ztics;        \
           set palette gray;   \
           set multiplot;      \
           set size .25,1;     \
           set origin 0,0;     \
           set xrange [0:5];   \
           set yrange [0:25];  \
           plot 't_space.dat' index i using 1:2:3 with labels left; \
           set autoscale;      \
           set size square 1;  \
           set origin .10, 0;  \
           plot 't_space.dat' index i+1 matrix with image; \
           unset multiplot;"


bind "Down" "i=i-2; \
             reset; \
             unset key; \
             unset colorbox; \
             unset border; \
             unset xtics; \
             unset ytics; \
             unset ztics; \
             set palette gray; \
             set multiplot; \
             set size .25,1; \
             set origin 0,0; \
             set xrange [0:5]; \
             set yrange [0:25]; \
             plot 't_space.dat' index i using 1:2:3 with labels left; \
             set autoscale; \
             set size square 1; \
             set origin .10, 0; \
             plot 't_space.dat' index i+1 matrix with image; \
             unset multiplot;"