# Poisson Library Routines

In addition to Real Discrete Trigonometric Transforms (TT) interface (refer to Trigonometric Transform Routines), Intel® MKL supports the Poisson Library interface, referred to as PL interface. The interface implements a group of routines (PL routines) used to compute a solution of Laplace, Poisson, and Helmholtz problems of special kind using discrete Fourier transforms. Laplace and Poisson problems are special cases of a more general Helmholtz problem. The problems being solved are defined more exactly in Poisson Library Implemented. The PL interface provides much flexibility of use: you can adjust routines to your particular needs at the cost of manual tuning routine parameters or just call routines with default parameter values. The interface can adjust style of error and warning messages to C or Fortran notations by setting up a dedicated parameter. This adds convenience to debugging, because users can read information in the way that is natural for their code. The Intel MKL PL interface currently contains only routines that implement the following solvers:

- Fast Laplace, Poisson and Helmholtz solvers in a Cartesian coordinate system
- Fast Poisson and Helmholtz solvers in a spherical coordinate system.

To describe the Intel MKL PL interface, the C convention is used. Fortran usage specifics can be found in Calling PDE Support Routines from Fortran 90.

### Note

Fortran users should mind that respective array indices in Fortran increase by 1.

- Poisson Library Implemented
- Sequence of Invoking PL Routines
- Interface Description
- PL Routines for the Cartesian Solver
- PL Routines for the Spherical Solver
- Common Parameters
- Implementation Details

Parent topic: Partial Differential Equations Support