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/*
* Multigrid solver for a 2nd order 2D linear PDE.
* Copyright 2018 Anton Khirnov <anton@khirnov.net>
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
#ifndef MG2D_H
#define MG2D_H
#include <stddef.h>
#include <stdint.h>
#include "mg2d_boundary.h"
#include "mg2d_constants.h"
typedef struct MG2DInternal MG2DInternal;
typedef struct MG2DContext {
/**
* Solver private data, not to be accessed in any way by the caller.
*/
MG2DInternal *priv;
/**
* A callback that will be used to print diagnostic messages.
*
* The default implementation prints to stderr.
*
* May be set to NULL to disable logging.
*/
void (*log_callback)(const struct MG2DContext *ctx, int level,
const char *fmt, va_list);
/**
* Arbitrary user data, e.g. to be used by the log callback.
*/
void *opaque;
/**
* Number of grid points in each direction, set by mg2d_solver_alloc().
* Read-only for the caller.
*/
size_t domain_size;
/**
* Distance between the neighbouring grid points.
* Must be set by the caller.
*/
double step[2];
/**
* Order of the finite difference operators used for approximating derivatives.
* Must be set by the caller.
*/
size_t fd_stencil;
/**
* Boundary specification, indexed by MG2DBoundaryLoc.
* To be filled by the caller.
*/
MG2DBoundary *boundaries[4];
/**
* Maximum number of solver iterations.
*/
unsigned int maxiter;
/**
* Value of the residual at which to consider the equation solved.
*/
double tol;
/**
* Number of cycles on each subgrid.
*/
unsigned int nb_cycles;
/**
* Number of relaxation steps before and after each coarser-grid solve.
*/
unsigned int nb_relax_pre;
unsigned int nb_relax_post;
/**
* Values of the unknown function.
*
* Allocated and initialized to zero by the solver in mg2d_solver_alloc(),
* owned by the solver.
* May be filled by the caller before solving to set the initial guess.
* Afterwards updated in mg2d_solve().
*/
double *u;
/**
* Distance between neighbouring gridpoints along coord1.
*/
ptrdiff_t u_stride;
/**
* Values of the right-hand side.
*
* Allocated by the solver in mg2d_solver_alloc(), owned by the solver.
* Must be filled by the caller before solving.
*/
double *rhs;
/**
* Distance between neighbouring gridpoints along coord1.
*/
ptrdiff_t rhs_stride;
/**
* Coefficients C_{*} that define the differential equation.
*
* Allocated by the solver in mg2d_solver_alloc(), owned by the solver.
* Must be filled by the caller before solving.
*/
double *diff_coeffs[MG2D_DIFF_COEFF_NB];
/**
* Distance between neighbouring gridpoints along coord1.
*/
ptrdiff_t diff_coeffs_stride;
/**
* Number of threads to use for processing.
*
* Set to 0 to autodetect. Defaults to 1.
*/
unsigned int nb_threads;
/**
* Time-stepping factor to use for relaxation.
*/
double cfl_factor;
/**
* Maximum level of messages printed by the default logging callback. Has no
* effect when log_callback is overridden.
*/
enum MG2DLogLevel log_level;
/**
* Maximum number of refinement levels. May only be modified by the caller
* before the first call to mg2d_solve().
*/
unsigned int max_levels;
/**
* Maximum size (along one dimensions) of a refinement level on which an
* exact solve is performed.
*/
size_t max_exact_size;
} MG2DContext;
/**
* Allocate the solver for the given domain size.
*
* @return The solver context on success, NULL on failure.
*/
MG2DContext *mg2d_solver_alloc(size_t domain_size);
/**
* Solve the equation, after all the required fields have been filled by the
* caller.
*
* This function may be called more than once.
*
* @return 0 on success, a negative error code on failure.
*/
int mg2d_solve(MG2DContext *ctx);
/**
* Free the solver and write NULL to the provided pointer.
*/
void mg2d_solver_free(MG2DContext **ctx);
/**
* Print the solver timing statistics using the logging callback.
*
* @param prefix the string prepended to each output line, may be NULL to mean
* none
*/
void mg2d_print_stats(MG2DContext *ctx, const char *prefix);
/**
* @return maximum supported value of fd_stencil.
*/
unsigned int mg2d_max_fd_stencil(void);
int mg2d_init_guess(MG2DContext *ctx, const double *src,
ptrdiff_t src_stride,
const size_t src_size[2],
const double src_step[2]);
#endif /* MG2D_H */
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