# Sample 2-d plot (derivative)

# You can run this by typing at the prompt: octave -q d2dplot.m

outfile = "d2dplot.dat";

# Note that octave will by default name the matrix "filename",
# but since variable names cannot start with a number it'll
# call this one "X2dplot" instead of "2dplot". We then take
# the numerical derivative and save.

load 2dplot.dat
z = X2dplot(:,1);
dz = diff(z);
points = [z(1:numel(z)-1) + dz(1)/2, diff(X2dplot(:,2))./dz];

fd = fopen(outfile, "wt");
fprintf(fd, "%14.6f %14.6f\n", \
        reshape(points', 1, numel(points)));
fclose(fd);
disp("Done!");