User-defined function syntax:
<func-name>( <dummy1> {,<dummy2>} ... {,<dummy5>} ) = <expression>
where 5#5expression6#6 is defined in terms of 5#5dummy16#6 through 5#5dummy56#6.
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 variable pi is already defined. But it is in no way magic; you may redefine it to be whatever you like. Some other variables may be defined under various gnuplot operations like mousing in interactive terminals or fitting; see gnuplot-defined variables (p. ) 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 "_".
See show functions (p. ), functions (p. ), gnuplot-defined variables (p. ), macros (p. ).