Software I like: gnuplot

To download, from the download page follow the link to the SourceForge download page and download, for example, gp463-win32-setup.exe for M$ Windows. When you run this installation programme, a long ‘important information’ text is displayed and a number of choices are offered whose meanings may not be clear even after reading the important information. You can just accept all of the default settings – things can be changed later. (You may want to deselect Associate gnuplot with the .plt file extension because the .plt file extension is often used by other software.) A second, even longer ‘important information’ text is displayed but it's just new features, changes and fixes since previous versions, so you can ignore it if this is your first time using gnuplot.

Note that the gnu in the name is not related to the GNU.

There's a lot of built-in help, although it can be a bit confusing until you get the drift.

• As a trivial example to get started, create a text file called gnuplot_test.gnuplot_data in some directory. (You can use something shorter than .gnuplot_data as the filename extension if you want.) Put a few lines of numbers into the file, two numbers per line, separated by spaces or tabs. For example,

  1 4
  2 6
  3 1
  4 7
  5 4
  

  Run gnuplot and click the Change Directory button in the toolbar. Browse to find the directory where you created your data file. Then type in the command plot "gnuplot_test.gnuplot_data" (note the quotation marks) followed by the Enter key. A window should pop up with a plot showing the individual data points.
• The results may be underwhelming if the default symbol type is + and several of the data points are hard to distinguish from the automatically scaled axes. To make the plot more visible, add lines between the points by giving the command set style data linespoints. Then use the up-arrow key to select the plot "gnuplot_test.gnuplot_data command again and use the Enter key to execute it.
• A set of commands can be stored in a file and then executed using the load command. If you're using trial and error to get the plot right and using the load command repeatedly, it seems to be a good idea to put a reset command at the beginning of your command file, to make sure leftover settings don't confuse things.
• Plotting output can be sent to a file in various formats as specified by an output device (or ‘terminal type’) such as svg, postscript, png. For example, to output to an SVG file, give commands like

  set terminal svg

  set output '\c:\users\username\filename.svg'

  To output to a .eps file, give commands like

  set terminal postscript eps

  set output '\c:\users\username\filename.eps'

  The screen corresponds to terminal type x11 under *n*x and wxt or windows under M$ Windows.
• Symbol types for plotting points are defined using an index number which unfortunately varies from device to device and is rather unorganized. If a symbol index is specified which is larger than the number supported by a particular device, the list of available symbols will be re-used in order; for example, if there are 13 available symbols and symbol type 16 is requested, then symbol type 3 will be used. Except for PostScript, the number of symbols available is very small and there is no built-in mechanism for adding additional symbols. (There are some clumsy work-arounds using character labels or images.) The following are the symbols available for a few terminals in gnuplot 4.6.3 (2013 Nov 10):
  • wxt
    
  • windows
    
  • png
    
  • svg
    
  • eps
    
  Note that I have not taken care to get consistent scaling from the different terminals, which does not happen automatically.
• Colours for the symbols are defined using the linetype index. For the terminal type windows I see:

  	windows	svg	png	x11*	postscript
  1	red	red	red	red
  2	green	dark green	green	green
  3	blue	blue	blue	blue
  4	magenta	cyan	magenta	magenta
  5	dark blue	dark cyan	cyan	cyan
  6	brown	dark blue	brown	brown
  7	dark cyan	light brown	yellow	dark yellow
  8	black	dark cyan	dark blue	pinkish
  9	dark grey	olive	dark yellow
  10	dark green	light blue	dark green
  11	olive	orange	mauve
  12	purple	purple	dark brown
  13	light grey	light green	pink
  14	cyan		green
  15	yellow		dark cyan
  16			...

  *The actual X11 colours may be different, depending on how your X11 resources are set.)
  A much more general mechanism (e.g., rgbcolor "red") is available from version 4.2; this avoids the horribly inconsistent device-dependence, for colours if not for symbol shapes.
• An SVG file created by gnuplot 4.0 could not be opened by either Inkscape 0.45 or Firefox 2.0 but could be opened by The GIMP 2.2.10. An SVG file created by gnuplot 4.2 can be opened by Inkscape and The GIMP, but not by Firefox; there seems to be a problem at the end of the file, with either no tag or some spurious null characters before the tag. Firefox also doesn't seem to handle some symbol types, although this may be a side-effect of the previous problem. The GIMP seems to have trouble getting the colours of symbols, and renders some of them black.