Computation of P-Functions on Plane Algebraic Curves

Numerical tools for computation of P-functions, also known as Kleinian, or multiply periodic, are proposed. In this connection, computation of periods of both the first and second kinds is reconsidered. An analytical approach to constructing Riemann surfaces of plane algebraic curves of low gonalities is used. The approach is based on explicit radical solutions to quadratic, cubic, and quartic equations, which serve for hyperelliptic, trigonal, and tetragonal curves, respectively. The proposed analytical models of Riemann surfaces give full control over computation of the Abel image of any point or divisor. Therefore, computation of P-functions at Abel images of given divisors can be done directly. An alternative computation with the help of the Jacobi inversion problem is used for verification. Hyperelliptic and trigonal curves are considered in detail, and illustrated by examples. A method of finding the unique characteristic corresponding to the vector of Riemann constants is suggested for non-hyperelliptic and hyperelliptic curves.