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New user-defined variables and functions of one through twelve variables may be declared and used anywhere, including on the plot command itself.
User-defined function syntax:
<func-name>( <dummy1> {,<dummy2>} ... {,<dummy12>} ) = <expression>
where <expression> is defined in terms of <dummy1> through <dummy12>. This form of function definition is limited to a single line. More complicated multi-line functions can be defined using the function block mechanism (new in this version). See function blocks.
User-defined variable syntax:
<variable-name> = <constant-expression>
Examples:
w = 2 q = floor(tan(pi/2 - 0.1)) f(x) = sin(w*x) sinc(x) = sin(pi*x)/(pi*x) delta(t) = (t == 0) ramp(t) = (t > 0) ? t : 0 min(a,b) = (a < b) ? a : b comb(n,k) = n!/(k!*(n-k)!) len3d(x,y,z) = sqrt(x*x+y*y+z*z) plot f(x) = sin(x*a), a = 0.2, f(x), a = 0.4, f(x)
file = "mydata.inp" file(n) = sprintf("run_%d.dat",n)
The final two examples illustrate a user-defined string variable and a user-defined string function.
Note that the variables pi (3.14159...) and NaN (IEEE "Not a Number") are already defined. You can redefine these to something else if you really need to. The original values can be recovered by setting:
NaN = GPVAL_NaN pi = GPVAL_pi
Other variables may be defined under various gnuplot operations like mousing in interactive terminals or fitting; see gnuplot-defined variables for details.
You can check for existence of a given variable V by the exists("V") expression. For example
a = 10 if (exists("a")) print "a is defined" if (!exists("b")) print "b is not defined"
Valid names are the same as in most programming languages: they must begin with a letter, but subsequent characters may be letters, digits, or "_".
Each function definition is made available as a special string-valued variable with the prefix 'GPFUN_'.
Example:
set label GPFUN_sinc at graph .05,.95
See show functions, functions, gnuplot-defined variables, macros, value.