General form:

.param <ident> = <expr>  <ident> = <expr> ...

Examples:

.param pippo=5
.param po=6 pp=7.8 pap={AGAUSS(pippo, 1, 1.67)}
.param pippp={pippo + pp}
.param p={pp}
.param pop='pp+p'

This line assigns numerical values to identifiers. More than one assignment per line is possible using a separating space. Parameter identifier names must begin with an alphabetic character. The other characters must be either alphabetic, a number, or ! # $ % [ ] _ as special characters. The variables time, temper, and hertz (see 5.1.1) are not valid identifier names. Other restrictions on naming conventions apply as well, see 2.8.6.

The .param lines inside subcircuits are copied per call, like any other line. All assignments are executed sequentially through the expanded circuit. Before its first use, a parameter name must have been assigned a value. Expressions defining a parameter should be put within braces {p+p2}, or alternatively within single quotes 'AGAUSS(pippo, 1, 1.67)'. An assignment cannot be self-referential, something like .param pip = 'pip+3' will not work.

The current ngspice version does not always need quotes or braces in expressions, especially when spaces are used sparingly. However, it is recommended to do so, as the following examples demonstrate.

.param a = 123 * 3    b = sqrt(9) $ doesn't work, a <= 123 
.param a = '123 * 3'  b = sqrt(9) $ ok.
.param c = a + 123   $ won't work
.param c = 'a + 123' $ ok. 
.param c = a+123     $ ok.