GLPK/Gnuplot

Gnuplot is a program for generating two and three dimensional plots of functions, data, and data fits. Gnuplot is published under the GNU General Public License. 2D histogram thumb|2D histogram generated with gnuplot from a GLPK solution Gnuplot expects data for histograms to be in multiple columns. The following example is based on examples/transp.mod from the GLPK source distribution: solve; printf '""' > 'transp1.dat'; printf {j in J} ' "%s"', j >> 'transp1.dat'; printf '\n' >> 'transp1.dat'; for {i in I} { printf '"%s"', i >> 'transp1.dat'; printf {j in J} ' %f', x[i,j] >> 'transp1.dat'; printf '\n' >> 'transp1.dat'; } The above MathProg statements (inserted before the data statements of transp.mod and saved as a file named transp1.mod) will create, using the command glpsol --math transp1.mod, the following content in the file transp1.dat: "" "New-York" "Chicago" "Topeka" "Seattle" 50.000000 300.000000 0.000000 "San-Diego" 275.000000 0.000000 275.000000 Using gnuplot, a histogram of transp1.dat can be drawn and then saved as a PNG image: reset set terminal png truecolor transparent font "Arial, 16" size 800x600 set output "transp1.png" set title 'Result of transp.mod' set style data histogram set style histogram cluster gap 1 set style fill solid border −1 set boxwidth 0.9 set bmargin 5 set grid y set xrange [−0.5:2.5] set xtics out nomirror plot 'transp1.dat' \ using 2:xtic(1) title columnheader(2), \ for [i=3:4] '' using i title columnheader(i) The above commands can either be hand entered into an interactive gnuplot session. Invoke gnuplot from the command-line to start such a session. Alternatively, the same commands can be saved in a text file transp1.gp and then run as a script from within gnuplot: gnuplot> load "transp1.gp" Finally, check the resulting transp1.png with any bitmap viewer, perhaps gthumb: gthumb transp1.png & 3D histogram thumb|3D histogram generated with gnuplot from a GLPK solution Gnuplot does not directly support native 3D histograms. Surfaces with rectangular grids can be passed to gnuplot using the following rules: provide one text line per point, with each field separated by a space consecutive points of one raster line should be on consecutive text lines place a blank text line between points of consecutive raster lines. To create a 3D histogram it is necessary to provide the 4 corner points of each pillar of the histogram. The following example is again based on examples/transp.mod: solve; printf '' > 'transp2.dat'; for { i in I } { for { j in J } { printf '%i "%s"', sum{k in I: k < i} 1, i >> 'transp2.dat'; printf ' %i "%s"', sum{l in J: l < j} 1, j >> 'transp2.dat'; printf ' %f', x[i,j] >> 'transp2.dat'; printf '\n' >> 'transp2.dat'; printf '%i "%s"', sum{k in I: k < i} 1, i >> 'transp2.dat'; printf ' %i "%s"', sum{l in J: l <= j} 1, '' >> 'transp2.dat'; printf ' %f', x[i,j] >> 'transp2.dat'; printf '\n' >> 'transp2.dat'; } printf '\n' >> 'transp2.dat'; for { j in J } { printf '%i "%s"', sum{k in I: k <= i} 1, '' >> 'transp2.dat'; printf ' %i "%s"', sum{l in J: l < j} 1, j >> 'transp2.dat'; printf ' %f', x[i,j] >> 'transp2.dat'; printf '\n' >> 'transp2.dat'; printf '%i "%s"', sum{k in I: k <= i} 1, '' >> 'transp2.dat'; printf ' %i "%s"', sum{l in J: l <= j} 1, '' >> 'transp2.dat'; printf ' %f', x[i,j] >> 'transp2.dat'; printf '\n' >> 'transp2.dat'; } printf '\n' >> 'transp2.dat'; } data; set I := San-Diego Seattle; set J := Chicago New-York Topeka; As before, a 3D histogram of transp2.dat can be drawn using gnuplot and saved as a PNG image: reset set terminal png font "Arial, 16" transparent size 800,800 set output "transp2.png" set title 'Result of transp.mod' set xtic offset first 0.5, first −0.25, first 0 mirror set ytic offset first 0.25, first 0.5, first 0 mirror set nokey set pm3d set palette gray set grid x y z splot 'transp2.dat' using 1:3:5:xtic(2):ytic(4) with pm3d