The Weierstrass sigma-function associated to a two-dimensional lattice is defined to be the product
where denotes .
The Weierstrass zeta-function is defined by the sum
Note that the Weierstrass zeta-function is basically the logarithmic derivative of the sigma-function. The zeta-function can be rewritten as:
where is the Eisenstein series of weight 2k + 2.
Also note that the derivative of the zeta-function is , where is the Weierstrass elliptic function
The Weierstrass zeta-function should not be confused with the Riemann zeta-function in number theory.
The Weierstrass eta-function is defined to be
It can be proved that this is well-defined, i.e. only depends on w. The Weierstrass eta-function should not be confused with the Dedekind eta-function.
The Weierstrass p-function is defined to be
The Weierstrass p-function is an even elliptic function of order N=2 with a double pole at each lattice and no others.