The mp driver produces output intended to be input to the Metapost program. Running Metapost on the file creates EPS files containing the plots. By default, Metapost passes all text through TeX. This has the advantage of allowing essentially any TeX symbols in titles and labels.
Syntax:
set term mp {color | colour | monochrome}
{solid | dashed}
{notex | tex | latex}
{magnification <magsize>}
{psnfss | psnfss-version7 | nopsnfss}
{prologues <value>}
{a4paper}
{amstex}
{"<fontname>"} {<fontsize>}
The option color causes lines to be drawn in color (on a printer or display that supports it), monochrome (or nothing) selects black lines. The option solid draws solid lines, while dashed (or nothing) selects lines with different patterns of dashes. If solid is selected but color is not, nearly all lines will be identical. This may occasionally be useful, so it is allowed.
The option notex bypasses TeX entirely, therefore no TeX code can be used in labels under this option. This is intended for use on old plot files or files that make frequent use of common characters like $ and % that require special handling in TeX.
The option tex sets the terminal to output its text for TeX to process.
The option latex sets the terminal to output its text for processing by LaTeX. This allows things like 3#3frac for fractions which LaTeX knows about but TeX does not. Note that you must set the environment variable TEX to the name of your LaTeX executable (normally latex) if you use this option or use mpost -tex=5#5name of LaTeX executable6#6 .... Otherwise metapost will try and use TeX to process the text and it won't work.
Changing font sizes in TeX has no effect on the size of mathematics, and there is no foolproof way to make such a change, except by globally setting a magnification factor. This is the purpose of the magnification option. It must be followed by a scaling factor. All text (NOT the graphs) will be scaled by this factor. Use this if you have math that you want at some size other than the default 10pt. Unfortunately, all math will be the same size, but see the discussion below on editing the MP output. mag will also work under notex but there seems no point in using it as the font size option (below) works as well.
The option psnfss uses postscript fonts in combination with LaTeX. Since this option only makes sense, if LaTeX is being used, the latex option is selected automatically. This option includes the following packages for LaTeX: inputenc(latin1), fontenc(T1), mathptmx, helvet(scaled=09.2), courier, latexsym and textcomp.
The option psnfss-version7 uses also postscript fonts in LaTeX (option latex is also automatically selected), but uses the following packages with LaTeX: inputenc(latin1), fontenc(T1), times, mathptmx, helvet and courier.
The option nopsnfss is the default and uses the standard font (cmr10 if not otherwise specified).
The option prologues takes a value as an additional argument and adds the line prologues:=5#5value6#6 to the metapost file. If a value of 2 is specified metapost uses postscript fonts to generate the eps-file, so that the result can be viewed using e.g. ghostscript. Normally the output of metapost uses TeX fonts and therefore has to be included in a (La)TeX file before you can look at it.
The option noprologues is the default. No additional line specifying the prologue will be added.
The option a4paper adds a [a4paper] to the documentclass. Normally letter paper is used (default). Since this option is only used in case of LaTeX, the latex option is selected automatically.
The option amstex automatically selects the latex option and includes the following LaTeX packages: amsfonts, amsmath(intlimits). By default these packages are not included.
A name in quotes selects the font that will be used when no explicit font is given in a set label or set title. A name recognized by TeX (a TFM file exists) must be used. The default is "cmr10" unless notex is selected, then it is "pcrr8r" (Courier). Even under notex, a TFM file is needed by Metapost. The file pcrr8r.tfm is the name given to Courier in LaTeX's psnfss package. If you change the font from the notex default, choose a font that matches the ASCII encoding at least in the range 32-126. cmtt10 almost works, but it has a nonblank character in position 32 (space).
The size can be any number between 5.0 and 99.99. If it is omitted, 10.0 is used. It is advisable to use magstep sizes: 10 times an integer or half-integer power of 1.2, rounded to two decimals, because those are the most available sizes of fonts in TeX systems.
All the options are optional. If font information is given, it must be at the end, with size (if present) last. The size is needed to select a size for the font, even if the font name includes size information. For example, set term mp "cmtt12" selects cmtt12 shrunk to the default size 10. This is probably not what you want or you would have used cmtt10.
The following common ascii characters need special treatment in TeX:
$, &, #, %, _; |, <, >; ^, ~, \, {, and }
If you type your labels inside double quotes, backslashes in TeX code need to be escaped (doubled). Using single quotes will avoid having to do this, but then you cannot use 3#3n for line breaks. As of this writing, version 3.7 of gnuplot processes titles given in a plot command differently than in other places, and backslashes in TeX commands need to be doubled regardless of the style of quotes.
Metapost pictures are typically used in TeX documents. Metapost deals with fonts pretty much the same way TeX does, which is different from most other document preparation programs. If the picture is included in a LaTeX document using the graphics package, or in a plainTeX document via epsf.tex, and then converted to PostScript with dvips (or other dvi-to-ps converter), the text in the plot will usually be handled correctly. However, the text may not appear if you send the Metapost output as-is to a PostScript interpreter.