8. MGL language

MathGL library supports the simplest scripts for data handling and plotting. These scripts can be used independently (with the help of UDAV, mgl2png, mgl2eps, mgl2svg programs and others, see section Utilities for parsing MGL) or in the frame of the library using.

MGL script language is rather simple. Each string is a command. First word of string is the name of command. Other words are command arguments. Command may have up to 1000 arguments (at least for now). Words are separated from each other by space or tabulation symbol. The upper or lower case of words is sufficient, i.e. variables a and A are different variables. Symbol ‘#’ starts the comment (all characters after # will be ignored). The exception is situation when ‘#’ is a part of some string. Also options can be specified after symbol ‘;’ (see section Command options (MGL)). Symbol ‘:’ starts new command (like new line character) if it is not placed inside a string or inside brackets.

If string contain references to external parameters (substrings ‘$0’, ‘$1’ ... ‘$9’) or definitions (substrings ‘$a’, ‘$b’ ... ‘$z’) then before execution the values of parameter/definition will be substituted instead of reference. It allows to use the same MGL script for different parameters (filenames, paths, condition and so on).

Argument can be a string, a variable name or a number.

• The string is any symbols between ordinary marks ‘'’.
• Usually variable have a name which is arbitrary combination of symbols (except spaces and ‘'’) started from a letter and with length less than 64. A temporary array can be used as variable:
  • sub-arrays (like in subdata command) as command argument. For example, a(1) or a(1,:) or a(1,:,:) is second row, a(:,2) or a(:,2,:) is third column, a(:,:,0) is first slice and so on. Also you can extract a part of array from m-th to n-th element by code a(m:n,:,:) or just a(m:n).
  • any column combinations defined by formulas, like a('n*w^2/exp(t)') if names for data columns was specified (by idset command or in the file at string started with ##).
  • any expression (without spaces) of existed variables produce temporary variable. For example, ‘sqrt(dat(:,5)+1)’ will produce temporary variable with data values equal to tmp[i,j] = sqrt(dat[i,5,j]+1).
  • temporary variable of higher dimensions by help of []. For example, ‘[1,2,3]’ will produce a temporary vector of 3 elements {1, 2, 3}; ‘[[11,12],[21,22]]’ will produce matrix 2*2 and so on. Here you can join even an arrays of the same dimensions by construction like ‘[v1,v2,...,vn]’.
  • result of code for making new data (see section Make another data (MGL)) inside {}. For example, ‘{sum dat 'x'}’ produce temporary variable which contain result of summation of dat along direction ’x’. This is the same array tmp as produced by command ‘sum tmp dat 'x'’. You can use nested constructions, like ‘{sum {max dat 'z'} 'x'}’.

  Temporary variables can not be used as 1st argument for commands which create (return) the data (like ‘new’, ‘read’, ‘hist’ and so on).

• Special names nan=#QNAN, pi=3.1415926..., on=1, off=0, :=-1 are treated as number if they were not redefined by user. Variables with suffixes are treated as numbers (see section Suffixes for variable). Names defined by define command are treated as number. Also results of formulas with sizes 1x1x1 are treated as number (for example, ‘pi/dat.nx’).

Before the first using all variables must be defined with the help of commands, like, new, var, list, copy, read, hist, sum and so on (see section Data create (MGL) and Make another data (MGL)).

Command may have several set of possible arguments (for example, plot ydat and plot xdat ydat). All command arguments for a selected set must be specified. However, some arguments can have default values. These argument are printed in [], like plot ydat ['stl'='' zval=nan]. At this, the record [arg1 arg2 arg3 ...] means [arg1 [arg2 [arg3 ...]]], i.e. you can omit only tailing arguments if you agree with its default values. For example, plot ydat '' 1 or plot ydat '' is correct, but plot ydat 1 is incorrect (argument 'stl' is missed).

All MGL commands can be divided on several groups. I will use the following notation for a command description: command names are bold, strings are denoted by commas, variable names are italic, numbers are typewriter. Optional arguments are placed in square brackets and default values for them are shown. Detailed description of color, line styles (see section Line styles), color schemes (see section Color scheme), font types, TeX-like symbols (see section Font styles) and formulas (see section Textual formulas) can be found in corresponding section.