a string with two characters among "s", "c",
"d" and "n"; this string specifies the function: the two
letters respectively denote the basic functions \(sn\), \(cn\),
\(dn\) and \(1\), and the string specifies the ratio of two such
functions, e.g. \(ns = 1/sn\) and \(cd = cn/dn\)
u
a complex number, vector or matrix
tau
complex number with strictly positive imaginary part; it is
related to m and only one of them must be supplied
m
the "parameter", square of the elliptic modulus; it is related to
tau and only one of them must be supplied