s21cbc evaluates the Jacobian elliptic functions
,
and
given by
where
is a complex argument,
is a real argument (the
modulus) with
and
(the
amplitude of
) is defined by the integral
The above definitions can be extended for values of
(see
Salzer (1962)) by means of the formulae
where
.
Special values include
These functions are often simply written as
,
and
, thereby avoiding explicit reference to the argument
. They can also be expressed in terms of Jacobian theta functions (see
s21ccc).
Another nine elliptic functions may be computed via the formulae
(see
Abramowitz and Stegun (1972)).
The values of
,
and
are obtained by calls to
s21cac. Further details can be found in
Section 9.
In principle the function is capable of achieving full relative precision in the computed values. However, the accuracy obtainable in practice depends on the accuracy of the standard elementary functions such as SIN and COS.
Background information to multithreading can be found in the
Multithreading documentation.
The values of
,
and
are computed via the formulae
where
and
(the
complementary modulus).