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Separate discretization and solver. Port Multigrid solver.

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This commit is contained in:
Jan Eitzinger
2024-03-04 14:29:49 +01:00
parent 4c0fefe1b5
commit 5a872d0533
15 changed files with 863 additions and 639 deletions
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435
BasicSolver/2D-seq/src/discretization.c Normal file
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@@ -0,0 +1,435 @@
/*
* Copyright (C) NHR@FAU, University Erlangen-Nuremberg.
* All rights reserved. This file is part of nusif-solver.
* Use of this source code is governed by a MIT style
* license that can be found in the LICENSE file.
*/
#include <float.h>
#include <math.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "allocate.h"
#include "discretization.h"
#include "parameter.h"
#include "util.h"
static void print(Discretization* d, double* grid)
{
int imax = d->grid.imax;
for (int j = 0; j < d->grid.jmax + 2; j++) {
printf("%02d: ", j);
for (int i = 0; i < d->grid.imax + 2; i++) {
printf("%12.8f ", grid[j * (imax + 2) + i]);
}
printf("\n");
}
fflush(stdout);
}
static void printConfig(Discretization* d)
{
printf("Parameters for #%s#\n", d->problem);
printf("Boundary conditions Left:%d Right:%d Bottom:%d Top:%d\n",
d->bcLeft,
d->bcRight,
d->bcBottom,
d->bcTop);
printf("\tReynolds number: %.2f\n", d->re);
printf("\tGx Gy: %.2f %.2f\n", d->gx, d->gy);
printf("Geometry data:\n");
printf("\tDomain box size (x, y): %.2f, %.2f\n", d->grid.xlength, d->grid.ylength);
printf("\tCells (x, y): %d, %d\n", d->grid.imax, d->grid.jmax);
printf("Timestep parameters:\n");
printf("\tDefault stepsize: %.2f, Final time %.2f\n", d->dt, d->te);
printf("\tdt bound: %.6f\n", d->dtBound);
printf("\tTau factor: %.2f\n", d->tau);
printf("Iterative d parameters:\n");
printf("\tgamma factor: %f\n", d->gamma);
}
void initDiscretization(Discretization* d, Parameter* p)
{
d->problem = p->name;
d->bcLeft = p->bcLeft;
d->bcRight = p->bcRight;
d->bcBottom = p->bcBottom;
d->bcTop = p->bcTop;
d->grid.imax = p->imax;
d->grid.jmax = p->jmax;
d->grid.xlength = p->xlength;
d->grid.ylength = p->ylength;
d->grid.dx = p->xlength / p->imax;
d->grid.dy = p->ylength / p->jmax;
d->re = p->re;
d->gx = p->gx;
d->gy = p->gy;
d->dt = p->dt;
d->te = p->te;
d->tau = p->tau;
d->gamma = p->gamma;
int imax = d->grid.imax;
int jmax = d->grid.jmax;
size_t size = (imax + 2) * (jmax + 2) * sizeof(double);
d->u = allocate(64, size);
d->v = allocate(64, size);
d->p = allocate(64, size);
d->rhs = allocate(64, size);
d->f = allocate(64, size);
d->g = allocate(64, size);
for (int i = 0; i < (imax + 2) * (jmax + 2); i++) {
d->u[i] = p->u_init;
d->v[i] = p->v_init;
d->p[i] = p->p_init;
d->rhs[i] = 0.0;
d->f[i] = 0.0;
d->g[i] = 0.0;
}
double dx = d->grid.dx;
double dy = d->grid.dy;
double invSqrSum = 1.0 / (dx * dx) + 1.0 / (dy * dy);
d->dtBound = 0.5 * d->re * 1.0 / invSqrSum;
#ifdef VERBOSE
printConfig(d);
#endif
}
void computeRHS(Discretization* d)
{
int imax = d->grid.imax;
int jmax = d->grid.jmax;
double idx = 1.0 / d->grid.dx;
double idy = 1.0 / d->grid.dy;
double idt = 1.0 / d->dt;
double* rhs = d->rhs;
double* f = d->f;
double* g = d->g;
for (int j = 1; j < jmax + 1; j++) {
for (int i = 1; i < imax + 1; i++) {
RHS(i, j) = idt *
((F(i, j) - F(i - 1, j)) * idx + (G(i, j) - G(i, j - 1)) * idy);
}
}
}
static double maxElement(Discretization* d, double* m)
{
int size = (d->grid.imax + 2) * (d->grid.jmax + 2);
double maxval = DBL_MIN;
for (int i = 0; i < size; i++) {
maxval = MAX(maxval, fabs(m[i]));
}
return maxval;
}
void normalizePressure(Discretization* d)
{
int size = (d->grid.imax + 2) * (d->grid.jmax + 2);
double* p = d->p;
double avgP = 0.0;
for (int i = 0; i < size; i++) {
avgP += p[i];
}
avgP /= size;
for (int i = 0; i < size; i++) {
p[i] = p[i] - avgP;
}
}
void computeTimestep(Discretization* d)
{
double dt = d->dtBound;
double dx = d->grid.dx;
double dy = d->grid.dy;
double umax = maxElement(d, d->u);
double vmax = maxElement(d, d->v);
if (umax > 0) {
dt = (dt > dx / umax) ? dx / umax : dt;
}
if (vmax > 0) {
dt = (dt > dy / vmax) ? dy / vmax : dt;
}
d->dt = dt * d->tau;
}
void setBoundaryConditions(Discretization* d)
{
int imax = d->grid.imax;
int jmax = d->grid.jmax;
double* u = d->u;
double* v = d->v;
// Left boundary
switch (d->bcLeft) {
case NOSLIP:
for (int j = 1; j < jmax + 1; j++) {
U(0, j) = 0.0;
V(0, j) = -V(1, j);
}
break;
case SLIP:
for (int j = 1; j < jmax + 1; j++) {
U(0, j) = 0.0;
V(0, j) = V(1, j);
}
break;
case OUTFLOW:
for (int j = 1; j < jmax + 1; j++) {
U(0, j) = U(1, j);
V(0, j) = V(1, j);
}
break;
case PERIODIC:
break;
}
// Right boundary
switch (d->bcRight) {
case NOSLIP:
for (int j = 1; j < jmax + 1; j++) {
U(imax, j) = 0.0;
V(imax + 1, j) = -V(imax, j);
}
break;
case SLIP:
for (int j = 1; j < jmax + 1; j++) {
U(imax, j) = 0.0;
V(imax + 1, j) = V(imax, j);
}
break;
case OUTFLOW:
for (int j = 1; j < jmax + 1; j++) {
U(imax, j) = U(imax - 1, j);
V(imax + 1, j) = V(imax, j);
}
break;
case PERIODIC:
break;
}
// Bottom boundary
switch (d->bcBottom) {
case NOSLIP:
for (int i = 1; i < imax + 1; i++) {
V(i, 0) = 0.0;
U(i, 0) = -U(i, 1);
}
break;
case SLIP:
for (int i = 1; i < imax + 1; i++) {
V(i, 0) = 0.0;
U(i, 0) = U(i, 1);
}
break;
case OUTFLOW:
for (int i = 1; i < imax + 1; i++) {
U(i, 0) = U(i, 1);
V(i, 0) = V(i, 1);
}
break;
case PERIODIC:
break;
}
// Top boundary
switch (d->bcTop) {
case NOSLIP:
for (int i = 1; i < imax + 1; i++) {
V(i, jmax) = 0.0;
U(i, jmax + 1) = -U(i, jmax);
}
break;
case SLIP:
for (int i = 1; i < imax + 1; i++) {
V(i, jmax) = 0.0;
U(i, jmax + 1) = U(i, jmax);
}
break;
case OUTFLOW:
for (int i = 1; i < imax + 1; i++) {
U(i, jmax + 1) = U(i, jmax);
V(i, jmax) = V(i, jmax - 1);
}
break;
case PERIODIC:
break;
}
}
void setSpecialBoundaryCondition(Discretization* d)
{
int imax = d->grid.imax;
int jmax = d->grid.jmax;
double mDy = d->grid.dy;
double* u = d->u;
if (strcmp(d->problem, "dcavity") == 0) {
for (int i = 1; i < imax; i++) {
U(i, jmax + 1) = 2.0 - U(i, jmax);
}
} else if (strcmp(d->problem, "canal") == 0) {
double ylength = d->grid.ylength;
double y;
for (int j = 1; j < jmax + 1; j++) {
y = mDy * (j - 0.5);
U(0, j) = y * (ylength - y) * 4.0 / (ylength * ylength);
}
}
}
void computeFG(Discretization* d)
{
double* u = d->u;
double* v = d->v;
double* f = d->f;
double* g = d->g;
int imax = d->grid.imax;
int jmax = d->grid.jmax;
double gx = d->gx;
double gy = d->gy;
double gamma = d->gamma;
double dt = d->dt;
double inverseRe = 1.0 / d->re;
double inverseDx = 1.0 / d->grid.dx;
double inverseDy = 1.0 / d->grid.dy;
double du2dx, dv2dy, duvdx, duvdy;
double du2dx2, du2dy2, dv2dx2, dv2dy2;
for (int j = 1; j < jmax + 1; j++) {
for (int i = 1; i < imax + 1; i++) {
du2dx = inverseDx * 0.25 *
((U(i, j) + U(i + 1, j)) * (U(i, j) + U(i + 1, j)) -
(U(i, j) + U(i - 1, j)) * (U(i, j) + U(i - 1, j))) +
gamma * inverseDx * 0.25 *
(fabs(U(i, j) + U(i + 1, j)) * (U(i, j) - U(i + 1, j)) +
fabs(U(i, j) + U(i - 1, j)) * (U(i, j) - U(i - 1, j)));
duvdy = inverseDy * 0.25 *
((V(i, j) + V(i + 1, j)) * (U(i, j) + U(i, j + 1)) -
(V(i, j - 1) + V(i + 1, j - 1)) * (U(i, j) + U(i, j - 1))) +
gamma * inverseDy * 0.25 *
(fabs(V(i, j) + V(i + 1, j)) * (U(i, j) - U(i, j + 1)) +
fabs(V(i, j - 1) + V(i + 1, j - 1)) *
(U(i, j) - U(i, j - 1)));
du2dx2 = inverseDx * inverseDx * (U(i + 1, j) - 2.0 * U(i, j) + U(i - 1, j));
du2dy2 = inverseDy * inverseDy * (U(i, j + 1) - 2.0 * U(i, j) + U(i, j - 1));
F(i, j) = U(i, j) + dt * (inverseRe * (du2dx2 + du2dy2) - du2dx - duvdy + gx);
duvdx = inverseDx * 0.25 *
((U(i, j) + U(i, j + 1)) * (V(i, j) + V(i + 1, j)) -
(U(i - 1, j) + U(i - 1, j + 1)) * (V(i, j) + V(i - 1, j))) +
gamma * inverseDx * 0.25 *
(fabs(U(i, j) + U(i, j + 1)) * (V(i, j) - V(i + 1, j)) +
fabs(U(i - 1, j) + U(i - 1, j + 1)) *
(V(i, j) - V(i - 1, j)));
dv2dy = inverseDy * 0.25 *
((V(i, j) + V(i, j + 1)) * (V(i, j) + V(i, j + 1)) -
(V(i, j) + V(i, j - 1)) * (V(i, j) + V(i, j - 1))) +
gamma * inverseDy * 0.25 *
(fabs(V(i, j) + V(i, j + 1)) * (V(i, j) - V(i, j + 1)) +
fabs(V(i, j) + V(i, j - 1)) * (V(i, j) - V(i, j - 1)));
dv2dx2 = inverseDx * inverseDx * (V(i + 1, j) - 2.0 * V(i, j) + V(i - 1, j));
dv2dy2 = inverseDy * inverseDy * (V(i, j + 1) - 2.0 * V(i, j) + V(i, j - 1));
G(i, j) = V(i, j) + dt * (inverseRe * (dv2dx2 + dv2dy2) - duvdx - dv2dy + gy);
}
}
/* ---------------------- boundary of F --------------------------- */
for (int j = 1; j < jmax + 1; j++) {
F(0, j) = U(0, j);
F(imax, j) = U(imax, j);
}
/* ---------------------- boundary of G --------------------------- */
for (int i = 1; i < imax + 1; i++) {
G(i, 0) = V(i, 0);
G(i, jmax) = V(i, jmax);
}
}
void adaptUV(Discretization* d)
{
int imax = d->grid.imax;
int jmax = d->grid.jmax;
double* p = d->p;
double* u = d->u;
double* v = d->v;
double* f = d->f;
double* g = d->g;
double factorX = d->dt / d->grid.dx;
double factorY = d->dt / d->grid.dy;
for (int j = 1; j < jmax + 1; j++) {
for (int i = 1; i < imax + 1; i++) {
U(i, j) = F(i, j) - (P(i + 1, j) - P(i, j)) * factorX;
V(i, j) = G(i, j) - (P(i, j + 1) - P(i, j)) * factorY;
}
}
}
void writeResult(Discretization* d)
{
int imax = d->grid.imax;
int jmax = d->grid.jmax;
double dx = d->grid.dx;
double dy = d->grid.dy;
double* p = d->p;
double* u = d->u;
double* v = d->v;
double x = 0.0, y = 0.0;
FILE* fp;
fp = fopen("pressure.dat", "w");
if (fp == NULL) {
printf("Error!\n");
exit(EXIT_FAILURE);
}
for (int j = 1; j < jmax + 1; j++) {
y = (double)(j - 0.5) * dy;
for (int i = 1; i < imax + 1; i++) {
x = (double)(i - 0.5) * dx;
fprintf(fp, "%.2f %.2f %f\n", x, y, P(i, j));
}
fprintf(fp, "\n");
}
fclose(fp);
fp = fopen("velocity.dat", "w");
if (fp == NULL) {
printf("Error!\n");
exit(EXIT_FAILURE);
}
for (int j = 1; j < jmax + 1; j++) {
y = dy * (j - 0.5);
for (int i = 1; i < imax + 1; i++) {
x = dx * (i - 0.5);
double velU = (U(i, j) + U(i - 1, j)) / 2.0;
double velV = (V(i, j) + V(i, j - 1)) / 2.0;
double len = sqrt((velU * velU) + (velV * velV));
fprintf(fp, "%.2f %.2f %f %f %f\n", x, y, velU, velV, len);
}
}
fclose(fp);
}

40
BasicSolver/2D-seq/src/discretization.h Normal file
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@@ -0,0 +1,40 @@
/*
* Copyright (C) NHR@FAU, University Erlangen-Nuremberg.
* All rights reserved. This file is part of nusif-solver.
* Use of this source code is governed by a MIT style
* license that can be found in the LICENSE file.
*/
#ifndef __DISCRETIZATION_H_
#define __DISCRETIZATION_H_
#include "grid.h"
#include "parameter.h"
enum BC { NOSLIP = 1, SLIP, OUTFLOW, PERIODIC };
typedef struct {
/* geometry and grid information */
Grid grid;
/* arrays */
double *p, *rhs;
double *f, *g;
double *u, *v;
/* parameters */
double re, tau, gamma;
double gx, gy;
/* time stepping */
double dt, te;
double dtBound;
char* problem;
int bcLeft, bcRight, bcBottom, bcTop;
} Discretization;
extern void initDiscretization(Discretization*, Parameter*);
extern void computeRHS(Discretization*);
extern void normalizePressure(Discretization*);
extern void computeTimestep(Discretization*);
extern void setBoundaryConditions(Discretization*);
extern void setSpecialBoundaryCondition(Discretization*);
extern void computeFG(Discretization*);
extern void adaptUV(Discretization*);
extern void writeResult(Discretization*);
#endif

51
BasicSolver/2D-seq/src/main.c
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@@ -4,12 +4,11 @@
* Use of this source code is governed by a MIT-style
* license that can be found in the LICENSE file.
*/
#include <float.h>
#include <limits.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include "discretization.h"
#include "parameter.h"
#include "progress.h"
#include "solver.h"
@@ -17,39 +16,41 @@
int main(int argc, char** argv)
{
double S, E;
Parameter params;
Solver solver;
initParameter(&params);
double timeStart, timeStop;
Parameter p;
Discretization d;
Solver s;
initParameter(&p);
if (argc != 2) {
printf("Usage: %s <configFile>\n", argv[0]);
exit(EXIT_SUCCESS);
}
readParameter(&params, argv[1]);
printParameter(&params);
initSolver(&solver, &params);
readParameter(&p, argv[1]);
printParameter(&p);
initDiscretization(&d, &p);
initSolver(&s, &d, &p);
#ifndef VERBOSE
initProgress(solver.te);
initProgress(d.te);
#endif
double tau = solver.tau;
double te = solver.te;
double tau = d.tau;
double te = d.te;
double t = 0.0;
int nt = 0;
S = getTimeStamp();
timeStart = getTimeStamp();
while (t <= te) {
if (tau > 0.0) computeTimestep(&solver);
setBoundaryConditions(&solver);
setSpecialBoundaryCondition(&solver);
computeFG(&solver);
computeRHS(&solver);
if (nt % 100 == 0) normalizePressure(&solver);
solveRB(&solver);
adaptUV(&solver);
t += solver.dt;
if (tau > 0.0) computeTimestep(&d);
setBoundaryConditions(&d);
setSpecialBoundaryCondition(&d);
computeFG(&d);
computeRHS(&d);
if (nt % 100 == 0) normalizePressure(&d);
solve(&s, d.p, d.rhs);
adaptUV(&d);
t += d.dt;
nt++;
#ifdef VERBOSE
@@ -58,9 +59,9 @@ int main(int argc, char** argv)
printProgress(t);
#endif
}
E = getTimeStamp();
timeStop = getTimeStamp();
stopProgress();
printf("Solution took %.2fs\n", E - S);
writeResult(&solver);
printf("Solution took %.2fs\n", timeStop - timeStart);
writeResult(&d);
return EXIT_SUCCESS;
}

6
BasicSolver/2D-seq/src/parameter.c
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@@ -24,6 +24,8 @@ void initParameter(Parameter* param)
param->re = 100.0;
param->gamma = 0.9;
param->tau = 0.5;
param->rho = 0.99;
param->levels = 5;
}
void readParameter(Parameter* param, const char* filename)
@@ -61,6 +63,7 @@ void readParameter(Parameter* param, const char* filename)
PARSE_INT(imax);
PARSE_INT(jmax);
PARSE_INT(itermax);
PARSE_INT(levels);
PARSE_REAL(eps);
PARSE_REAL(omg);
PARSE_REAL(re);
@@ -78,6 +81,7 @@ void readParameter(Parameter* param, const char* filename)
PARSE_REAL(u_init);
PARSE_REAL(v_init);
PARSE_REAL(p_init);
PARSE_REAL(rho);
}
}
@@ -108,4 +112,6 @@ void printParameter(Parameter* param)
printf("\tepsilon (stopping tolerance) : %f\n", param->eps);
printf("\tgamma (stopping tolerance) : %f\n", param->gamma);
printf("\tomega (SOR relaxation): %f\n", param->omg);
printf("\trho (SOR relaxation): %f\n", param->rho);
printf("\tMultiGrid levels : %d\n", param->levels);
}

4
BasicSolver/2D-seq/src/parameter.h
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@@ -10,8 +10,8 @@
typedef struct {
double xlength, ylength;
int imax, jmax;
int itermax;
double eps, omg;
int itermax, levels;
double eps, omg, rho;
double re, tau, gamma;
double te, dt;
double gx, gy;

192
BasicSolver/2D-seq/src/solver-mg.c Normal file
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@@ -0,0 +1,192 @@
/*
* Copyright (C) NHR@FAU, University Erlangen-Nuremberg.
* All rights reserved. This file is part of nusif-solver.
* Use of this source code is governed by a MIT style
* license that can be found in the LICENSE file.
*/
#include <stdio.h>
#include <stdlib.h>
#include "allocate.h"
#include "discretization.h"
#include "parameter.h"
#include "solver.h"
#include "util.h"
#define FINEST_LEVEL 0
#define S(i, j) s[(j) * (imax + 2) + (i)]
#define E(i, j) e[(j) * (imax + 2) + (i)]
#define R(i, j) r[(j) * (imax + 2) + (i)]
#define OLD(i, j) old[(j) * (imax + 2) + (i)]
static void restrictMG(Solver* s, int level, int imax, int jmax)
{
double* r = s->r[level + 1];
double* old = s->r[level];
for (int j = 1; j < jmax + 1; j++) {
for (int i = 1; i < imax + 1; i++) {
R(i, j) = (OLD(2 * i - 1, 2 * j - 1) + OLD(2 * i, 2 * j - 1) * 2 +
OLD(2 * i + 1, 2 * j - 1) + OLD(2 * i - 1, 2 * j) * 2 +
OLD(2 * i, 2 * j) * 4 + OLD(2 * i + 1, 2 * j) * 2 +
OLD(2 * i - 1, 2 * j + 1) + OLD(2 * i, 2 * j + 1) * 2 +
OLD(2 * i + 1, 2 * j + 1)) /
16.0;
}
}
}
static void prolongate(Solver* s, int level, int imax, int jmax)
{
double* old = s->r[level + 1];
double* e = s->r[level];
for (int j = 2; j < jmax + 1; j += 2) {
for (int i = 2; i < imax + 1; i += 2) {
E(i, j) = OLD(i / 2, j / 2);
}
}
}
static void correct(Solver* s, double* p, int level, int imax, int jmax)
{
double* e = s->e[level];
for (int j = 1; j < jmax + 1; ++j) {
for (int i = 1; i < imax + 1; ++i) {
P(i, j) += E(i, j);
}
}
}
static void setBoundaryCondition(double* p, int imax, int jmax)
{
for (int i = 1; i < imax + 1; i++) {
P(i, 0) = P(i, 1);
P(i, jmax + 1) = P(i, jmax);
}
for (int j = 1; j < jmax + 1; j++) {
P(0, j) = P(1, j);
P(imax + 1, j) = P(imax, j);
}
}
static double smooth(Solver* s, double* p, double* rhs, int level, int imax, int jmax)
{
double dx2 = s->grid->dx * s->grid->dx;
double dy2 = s->grid->dy * s->grid->dy;
double idx2 = 1.0 / dx2;
double idy2 = 1.0 / dy2;
double factor = s->omega * 0.5 * (dx2 * dy2) / (dx2 + dy2);
double* r = s->r[level];
double res = 1.0;
int pass, jsw, isw;
jsw = 1;
for (pass = 0; pass < 2; pass++) {
isw = jsw;
for (int j = 1; j < jmax + 1; j++) {
for (int i = isw; i < imax + 1; i += 2) {
R(i, j) = RHS(i, j) -
((P(i + 1, j) - 2.0 * P(i, j) + P(i - 1, j)) * idx2 +
(P(i, j + 1) - 2.0 * P(i, j) + P(i, j - 1)) * idy2);
P(i, j) -= (factor * R(i, j));
res += (R(i, j) * R(i, j));
}
isw = 3 - isw;
}
jsw = 3 - jsw;
}
res = res / (double)(imax * jmax);
return res;
}
void initSolver(Solver* s, Discretization* d, Parameter* p)
{
s->eps = p->eps;
s->omega = p->omg;
s->itermax = p->itermax;
s->rho = p->rho;
s->levels = p->levels;
s->grid = &d->grid;
int imax = s->grid->imax;
int jmax = s->grid->jmax;
int levels = s->levels;
printf("Using Multigrid solver with %d levels\n", levels);
s->r = malloc(levels * sizeof(double*));
s->e = malloc(levels * sizeof(double*));
size_t size = (imax + 2) * (jmax + 2) * sizeof(double);
for (int j = 0; j < levels; j++) {
s->r[j] = allocate(64, size);
s->e[j] = allocate(64, size);
for (int i = 0; i < (imax + 2) * (jmax + 2); i++) {
s->r[j][i] = 0.0;
s->e[j][i] = 0.0;
}
}
}
double multiGrid(Solver* solver, double* p, double* rhs, int level, int imax, int jmax)
{
double res = 0.0;
// coarsest level TODO: Use direct solver?
if (level == (solver->levels - 1)) {
for (int i = 0; i < 5; i++) {
smooth(solver, p, rhs, level, imax, jmax);
}
return res;
}
// pre-smoothing TODO: Make smoothing steps configurable?
for (int i = 0; i < 5; i++) {
smooth(solver, p, rhs, level, imax, jmax);
if (level == FINEST_LEVEL) setBoundaryCondition(p, imax, jmax);
}
// restrict
restrictMG(solver, level, imax, jmax);
// MGSolver on residual and error.
// TODO: What if there is a rest?
multiGrid(solver,
solver->e[level + 1],
solver->r[level],
level + 1,
imax / 2,
jmax / 2);
// prolongate
prolongate(solver, level, imax, jmax);
// correct p on finer level using residual
correct(solver, p, level, imax, jmax);
if (level == FINEST_LEVEL) setBoundaryCondition(p, imax, jmax);
// post-smoothing
for (int i = 0; i < 5; i++) {
res = smooth(solver, p, rhs, level, imax, jmax);
if (level == FINEST_LEVEL) setBoundaryCondition(p, imax, jmax);
}
return res;
}
void solve(Solver* s, double* p, double* rhs)
{
double res = multiGrid(s, p, rhs, 0, s->grid->imax, s->grid->jmax);
#ifdef VERBOSE
printf("Residuum: %.6f\n", res);
#endif
}

129
BasicSolver/2D-seq/src/solver-sor.c Normal file
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/*
* Copyright (C) NHR@FAU, University Erlangen-Nuremberg.
* All rights reserved. This file is part of nusif-solver.
* Use of this source code is governed by a MIT style
* license that can be found in the LICENSE file.
*/
#include "discretization.h"
#include "solver.h"
#include "util.h"
void initSolver(Solver* s, Discretization* d, Parameter* p)
{
s->grid = &d->grid;
s->itermax = p->itermax;
s->eps = p->eps;
s->omega = p->omg;
}
void solveSOR(Solver* solver, double* p, double* rhs)
{
int imax = solver->grid->imax;
int jmax = solver->grid->jmax;
double eps = solver->eps;
int itermax = solver->itermax;
double dx2 = solver->grid->dx * solver->grid->dx;
double dy2 = solver->grid->dy * solver->grid->dy;
double idx2 = 1.0 / dx2;
double idy2 = 1.0 / dy2;
double factor = solver->omega * 0.5 * (dx2 * dy2) / (dx2 + dy2);
double epssq = eps * eps;
int it = 0;
double res = 1.0;
while ((res >= epssq) && (it < itermax)) {
res = 0.0;
for (int j = 1; j < jmax + 1; j++) {
for (int i = 1; i < imax + 1; i++) {
double r = RHS(i, j) -
((P(i + 1, j) - 2.0 * P(i, j) + P(i - 1, j)) * idx2 +
(P(i, j + 1) - 2.0 * P(i, j) + P(i, j - 1)) * idy2);
P(i, j) -= (factor * r);
res += (r * r);
}
}
for (int i = 1; i < imax + 1; i++) {
P(i, 0) = P(i, 1);
P(i, jmax + 1) = P(i, jmax);
}
for (int j = 1; j < jmax + 1; j++) {
P(0, j) = P(1, j);
P(imax + 1, j) = P(imax, j);
}
res = res / (double)(imax * jmax);
#ifdef DEBUG
printf("%d Residuum: %e\n", it, res);
#endif
it++;
}
#ifdef VERBOSE
printf("Solver took %d iterations to reach %f\n", it, sqrt(res));
#endif
}
void solve(Solver* solver, double* p, double* rhs)
{
int imax = solver->grid->imax;
int jmax = solver->grid->jmax;
double eps = solver->eps;
int itermax = solver->itermax;
double dx2 = solver->grid->dx * solver->grid->dx;
double dy2 = solver->grid->dy * solver->grid->dy;
double idx2 = 1.0 / dx2;
double idy2 = 1.0 / dy2;
double factor = solver->omega * 0.5 * (dx2 * dy2) / (dx2 + dy2);
double epssq = eps * eps;
int it = 0;
double res = 1.0;
int pass, jsw, isw;
while ((res >= epssq) && (it < itermax)) {
res = 0.0;
jsw = 1;
for (pass = 0; pass < 2; pass++) {
isw = jsw;
for (int j = 1; j < jmax + 1; j++) {
for (int i = isw; i < imax + 1; i += 2) {
double r = RHS(i, j) -
((P(i + 1, j) - 2.0 * P(i, j) + P(i - 1, j)) * idx2 +
(P(i, j + 1) - 2.0 * P(i, j) + P(i, j - 1)) * idy2);
P(i, j) -= (factor * r);
res += (r * r);
}
isw = 3 - isw;
}
jsw = 3 - jsw;
}
for (int i = 1; i < imax + 1; i++) {
P(i, 0) = P(i, 1);
P(i, jmax + 1) = P(i, jmax);
}
for (int j = 1; j < jmax + 1; j++) {
P(0, j) = P(1, j);
P(imax + 1, j) = P(imax, j);
}
res = res / (double)(imax * jmax);
#ifdef DEBUG
printf("%d Residuum: %e\n", it, res);
#endif
it++;
}
#ifdef VERBOSE
printf("Solver took %d iterations to reach %f\n", it, sqrt(res));
#endif
}

564
BasicSolver/2D-seq/src/solver.c
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@@ -1,564 +0,0 @@
/*
* Copyright (C) NHR@FAU, University Erlangen-Nuremberg.
* All rights reserved. This file is part of nusif-solver.
* Use of this source code is governed by a MIT style
* license that can be found in the LICENSE file.
*/
#include <float.h>
#include <math.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "allocate.h"
#include "parameter.h"
#include "solver.h"
#include "util.h"
#define P(i, j) p[(j) * (imax + 2) + (i)]
#define F(i, j) f[(j) * (imax + 2) + (i)]
#define G(i, j) g[(j) * (imax + 2) + (i)]
#define U(i, j) u[(j) * (imax + 2) + (i)]
#define V(i, j) v[(j) * (imax + 2) + (i)]
#define RHS(i, j) rhs[(j) * (imax + 2) + (i)]
static void print(Solver* solver, double* grid)
{
int imax = solver->imax;
for (int j = 0; j < solver->jmax + 2; j++) {
printf("%02d: ", j);
for (int i = 0; i < solver->imax + 2; i++) {
printf("%12.8f ", grid[j * (imax + 2) + i]);
}
printf("\n");
}
fflush(stdout);
}
static void printConfig(Solver* solver)
{
printf("Parameters for #%s#\n", solver->problem);
printf("Boundary conditions Left:%d Right:%d Bottom:%d Top:%d\n",
solver->bcLeft,
solver->bcRight,
solver->bcBottom,
solver->bcTop);
printf("\tReynolds number: %.2f\n", solver->re);
printf("\tGx Gy: %.2f %.2f\n", solver->gx, solver->gy);
printf("Geometry data:\n");
printf("\tDomain box size (x, y): %.2f, %.2f\n", solver->xlength, solver->ylength);
printf("\tCells (x, y): %d, %d\n", solver->imax, solver->jmax);
printf("Timestep parameters:\n");
printf("\tDefault stepsize: %.2f, Final time %.2f\n", solver->dt, solver->te);
printf("\tdt bound: %.6f\n", solver->dtBound);
printf("\tTau factor: %.2f\n", solver->tau);
printf("Iterative solver parameters:\n");
printf("\tMax iterations: %d\n", solver->itermax);
printf("\tepsilon (stopping tolerance) : %f\n", solver->eps);
printf("\tgamma factor: %f\n", solver->gamma);
printf("\tomega (SOR relaxation): %f\n", solver->omega);
}
void initSolver(Solver* solver, Parameter* params)
{
solver->problem = params->name;
solver->bcLeft = params->bcLeft;
solver->bcRight = params->bcRight;
solver->bcBottom = params->bcBottom;
solver->bcTop = params->bcTop;
solver->imax = params->imax;
solver->jmax = params->jmax;
solver->xlength = params->xlength;
solver->ylength = params->ylength;
solver->dx = params->xlength / params->imax;
solver->dy = params->ylength / params->jmax;
solver->eps = params->eps;
solver->omega = params->omg;
solver->itermax = params->itermax;
solver->re = params->re;
solver->gx = params->gx;
solver->gy = params->gy;
solver->dt = params->dt;
solver->te = params->te;
solver->tau = params->tau;
solver->gamma = params->gamma;
int imax = solver->imax;
int jmax = solver->jmax;
size_t size = (imax + 2) * (jmax + 2) * sizeof(double);
solver->u = allocate(64, size);
solver->v = allocate(64, size);
solver->p = allocate(64, size);
solver->rhs = allocate(64, size);
solver->f = allocate(64, size);
solver->g = allocate(64, size);
for (int i = 0; i < (imax + 2) * (jmax + 2); i++) {
solver->u[i] = params->u_init;
solver->v[i] = params->v_init;
solver->p[i] = params->p_init;
solver->rhs[i] = 0.0;
solver->f[i] = 0.0;
solver->g[i] = 0.0;
}
double dx = solver->dx;
double dy = solver->dy;
double invSqrSum = 1.0 / (dx * dx) + 1.0 / (dy * dy);
solver->dtBound = 0.5 * solver->re * 1.0 / invSqrSum;
#ifdef VERBOSE
printConfig(solver);
#endif
}
void computeRHS(Solver* solver)
{
int imax = solver->imax;
int jmax = solver->jmax;
double idx = 1.0 / solver->dx;
double idy = 1.0 / solver->dy;
double idt = 1.0 / solver->dt;
double* rhs = solver->rhs;
double* f = solver->f;
double* g = solver->g;
for (int j = 1; j < jmax + 1; j++) {
for (int i = 1; i < imax + 1; i++) {
RHS(i, j) = idt *
((F(i, j) - F(i - 1, j)) * idx + (G(i, j) - G(i, j - 1)) * idy);
}
}
}
void solve(Solver* solver)
{
int imax = solver->imax;
int jmax = solver->jmax;
double eps = solver->eps;
int itermax = solver->itermax;
double dx2 = solver->dx * solver->dx;
double dy2 = solver->dy * solver->dy;
double idx2 = 1.0 / dx2;
double idy2 = 1.0 / dy2;
double factor = solver->omega * 0.5 * (dx2 * dy2) / (dx2 + dy2);
double* p = solver->p;
double* rhs = solver->rhs;
double epssq = eps * eps;
int it = 0;
double res = 1.0;
while ((res >= epssq) && (it < itermax)) {
res = 0.0;
for (int j = 1; j < jmax + 1; j++) {
for (int i = 1; i < imax + 1; i++) {
double r = RHS(i, j) -
((P(i + 1, j) - 2.0 * P(i, j) + P(i - 1, j)) * idx2 +
(P(i, j + 1) - 2.0 * P(i, j) + P(i, j - 1)) * idy2);
P(i, j) -= (factor * r);
res += (r * r);
}
}
for (int i = 1; i < imax + 1; i++) {
P(i, 0) = P(i, 1);
P(i, jmax + 1) = P(i, jmax);
}
for (int j = 1; j < jmax + 1; j++) {
P(0, j) = P(1, j);
P(imax + 1, j) = P(imax, j);
}
res = res / (double)(imax * jmax);
#ifdef DEBUG
printf("%d Residuum: %e\n", it, res);
#endif
it++;
}
#ifdef VERBOSE
printf("Solver took %d iterations to reach %f\n", it, sqrt(res));
#endif
}
void solveRB(Solver* solver)
{
int imax = solver->imax;
int jmax = solver->jmax;
double eps = solver->eps;
int itermax = solver->itermax;
double dx2 = solver->dx * solver->dx;
double dy2 = solver->dy * solver->dy;
double idx2 = 1.0 / dx2;
double idy2 = 1.0 / dy2;
double factor = solver->omega * 0.5 * (dx2 * dy2) / (dx2 + dy2);
double* p = solver->p;
double* rhs = solver->rhs;
double epssq = eps * eps;
int it = 0;
double res = 1.0;
int pass, jsw, isw;
while ((res >= epssq) && (it < itermax)) {
res = 0.0;
jsw = 1;
for (pass = 0; pass < 2; pass++) {
isw = jsw;
for (int j = 1; j < jmax + 1; j++) {
for (int i = isw; i < imax + 1; i += 2) {
double r = RHS(i, j) -
((P(i + 1, j) - 2.0 * P(i, j) + P(i - 1, j)) * idx2 +
(P(i, j + 1) - 2.0 * P(i, j) + P(i, j - 1)) * idy2);
P(i, j) -= (factor * r);
res += (r * r);
}
isw = 3 - isw;
}
jsw = 3 - jsw;
}
for (int i = 1; i < imax + 1; i++) {
P(i, 0) = P(i, 1);
P(i, jmax + 1) = P(i, jmax);
}
for (int j = 1; j < jmax + 1; j++) {
P(0, j) = P(1, j);
P(imax + 1, j) = P(imax, j);
}
res = res / (double)(imax * jmax);
#ifdef DEBUG
printf("%d Residuum: %e\n", it, res);
#endif
it++;
}
#ifdef VERBOSE
printf("Solver took %d iterations to reach %f\n", it, sqrt(res));
#endif
}
static double maxElement(Solver* solver, double* m)
{
int size = (solver->imax + 2) * (solver->jmax + 2);
double maxval = DBL_MIN;
for (int i = 0; i < size; i++) {
maxval = MAX(maxval, fabs(m[i]));
}
return maxval;
}
void normalizePressure(Solver* solver)
{
int size = (solver->imax + 2) * (solver->jmax + 2);
double* p = solver->p;
double avgP = 0.0;
for (int i = 0; i < size; i++) {
avgP += p[i];
}
avgP /= size;
for (int i = 0; i < size; i++) {
p[i] = p[i] - avgP;
}
}
void computeTimestep(Solver* solver)
{
double dt = solver->dtBound;
double dx = solver->dx;
double dy = solver->dy;
double umax = maxElement(solver, solver->u);
double vmax = maxElement(solver, solver->v);
if (umax > 0) {
dt = (dt > dx / umax) ? dx / umax : dt;
}
if (vmax > 0) {
dt = (dt > dy / vmax) ? dy / vmax : dt;
}
solver->dt = dt * solver->tau;
}
void setBoundaryConditions(Solver* solver)
{
int imax = solver->imax;
int jmax = solver->jmax;
double* u = solver->u;
double* v = solver->v;
// Left boundary
switch (solver->bcLeft) {
case NOSLIP:
for (int j = 1; j < jmax + 1; j++) {
U(0, j) = 0.0;
V(0, j) = -V(1, j);
}
break;
case SLIP:
for (int j = 1; j < jmax + 1; j++) {
U(0, j) = 0.0;
V(0, j) = V(1, j);
}
break;
case OUTFLOW:
for (int j = 1; j < jmax + 1; j++) {
U(0, j) = U(1, j);
V(0, j) = V(1, j);
}
break;
case PERIODIC:
break;
}
// Right boundary
switch (solver->bcRight) {
case NOSLIP:
for (int j = 1; j < jmax + 1; j++) {
U(imax, j) = 0.0;
V(imax + 1, j) = -V(imax, j);
}
break;
case SLIP:
for (int j = 1; j < jmax + 1; j++) {
U(imax, j) = 0.0;
V(imax + 1, j) = V(imax, j);
}
break;
case OUTFLOW:
for (int j = 1; j < jmax + 1; j++) {
U(imax, j) = U(imax - 1, j);
V(imax + 1, j) = V(imax, j);
}
break;
case PERIODIC:
break;
}
// Bottom boundary
switch (solver->bcBottom) {
case NOSLIP:
for (int i = 1; i < imax + 1; i++) {
V(i, 0) = 0.0;
U(i, 0) = -U(i, 1);
}
break;
case SLIP:
for (int i = 1; i < imax + 1; i++) {
V(i, 0) = 0.0;
U(i, 0) = U(i, 1);
}
break;
case OUTFLOW:
for (int i = 1; i < imax + 1; i++) {
U(i, 0) = U(i, 1);
V(i, 0) = V(i, 1);
}
break;
case PERIODIC:
break;
}
// Top boundary
switch (solver->bcTop) {
case NOSLIP:
for (int i = 1; i < imax + 1; i++) {
V(i, jmax) = 0.0;
U(i, jmax + 1) = -U(i, jmax);
}
break;
case SLIP:
for (int i = 1; i < imax + 1; i++) {
V(i, jmax) = 0.0;
U(i, jmax + 1) = U(i, jmax);
}
break;
case OUTFLOW:
for (int i = 1; i < imax + 1; i++) {
U(i, jmax + 1) = U(i, jmax);
V(i, jmax) = V(i, jmax - 1);
}
break;
case PERIODIC:
break;
}
}
void setSpecialBoundaryCondition(Solver* solver)
{
int imax = solver->imax;
int jmax = solver->jmax;
double mDy = solver->dy;
double* u = solver->u;
if (strcmp(solver->problem, "dcavity") == 0) {
for (int i = 1; i < imax; i++) {
U(i, jmax + 1) = 2.0 - U(i, jmax);
}
} else if (strcmp(solver->problem, "canal") == 0) {
double ylength = solver->ylength;
double y;
for (int j = 1; j < jmax + 1; j++) {
y = mDy * (j - 0.5);
U(0, j) = y * (ylength - y) * 4.0 / (ylength * ylength);
}
}
}
void computeFG(Solver* solver)
{
double* u = solver->u;
double* v = solver->v;
double* f = solver->f;
double* g = solver->g;
int imax = solver->imax;
int jmax = solver->jmax;
double gx = solver->gx;
double gy = solver->gy;
double gamma = solver->gamma;
double dt = solver->dt;
double inverseRe = 1.0 / solver->re;
double inverseDx = 1.0 / solver->dx;
double inverseDy = 1.0 / solver->dy;
double du2dx, dv2dy, duvdx, duvdy;
double du2dx2, du2dy2, dv2dx2, dv2dy2;
for (int j = 1; j < jmax + 1; j++) {
for (int i = 1; i < imax + 1; i++) {
du2dx = inverseDx * 0.25 *
((U(i, j) + U(i + 1, j)) * (U(i, j) + U(i + 1, j)) -
(U(i, j) + U(i - 1, j)) * (U(i, j) + U(i - 1, j))) +
gamma * inverseDx * 0.25 *
(fabs(U(i, j) + U(i + 1, j)) * (U(i, j) - U(i + 1, j)) +
fabs(U(i, j) + U(i - 1, j)) * (U(i, j) - U(i - 1, j)));
duvdy = inverseDy * 0.25 *
((V(i, j) + V(i + 1, j)) * (U(i, j) + U(i, j + 1)) -
(V(i, j - 1) + V(i + 1, j - 1)) * (U(i, j) + U(i, j - 1))) +
gamma * inverseDy * 0.25 *
(fabs(V(i, j) + V(i + 1, j)) * (U(i, j) - U(i, j + 1)) +
fabs(V(i, j - 1) + V(i + 1, j - 1)) *
(U(i, j) - U(i, j - 1)));
du2dx2 = inverseDx * inverseDx * (U(i + 1, j) - 2.0 * U(i, j) + U(i - 1, j));
du2dy2 = inverseDy * inverseDy * (U(i, j + 1) - 2.0 * U(i, j) + U(i, j - 1));
F(i, j) = U(i, j) + dt * (inverseRe * (du2dx2 + du2dy2) - du2dx - duvdy + gx);
duvdx = inverseDx * 0.25 *
((U(i, j) + U(i, j + 1)) * (V(i, j) + V(i + 1, j)) -
(U(i - 1, j) + U(i - 1, j + 1)) * (V(i, j) + V(i - 1, j))) +
gamma * inverseDx * 0.25 *
(fabs(U(i, j) + U(i, j + 1)) * (V(i, j) - V(i + 1, j)) +
fabs(U(i - 1, j) + U(i - 1, j + 1)) *
(V(i, j) - V(i - 1, j)));
dv2dy = inverseDy * 0.25 *
((V(i, j) + V(i, j + 1)) * (V(i, j) + V(i, j + 1)) -
(V(i, j) + V(i, j - 1)) * (V(i, j) + V(i, j - 1))) +
gamma * inverseDy * 0.25 *
(fabs(V(i, j) + V(i, j + 1)) * (V(i, j) - V(i, j + 1)) +
fabs(V(i, j) + V(i, j - 1)) * (V(i, j) - V(i, j - 1)));
dv2dx2 = inverseDx * inverseDx * (V(i + 1, j) - 2.0 * V(i, j) + V(i - 1, j));
dv2dy2 = inverseDy * inverseDy * (V(i, j + 1) - 2.0 * V(i, j) + V(i, j - 1));
G(i, j) = V(i, j) + dt * (inverseRe * (dv2dx2 + dv2dy2) - duvdx - dv2dy + gy);
}
}
/* ---------------------- boundary of F --------------------------- */
for (int j = 1; j < jmax + 1; j++) {
F(0, j) = U(0, j);
F(imax, j) = U(imax, j);
}
/* ---------------------- boundary of G --------------------------- */
for (int i = 1; i < imax + 1; i++) {
G(i, 0) = V(i, 0);
G(i, jmax) = V(i, jmax);
}
}
void adaptUV(Solver* solver)
{
int imax = solver->imax;
int jmax = solver->jmax;
double* p = solver->p;
double* u = solver->u;
double* v = solver->v;
double* f = solver->f;
double* g = solver->g;
double factorX = solver->dt / solver->dx;
double factorY = solver->dt / solver->dy;
for (int j = 1; j < jmax + 1; j++) {
for (int i = 1; i < imax + 1; i++) {
U(i, j) = F(i, j) - (P(i + 1, j) - P(i, j)) * factorX;
V(i, j) = G(i, j) - (P(i, j + 1) - P(i, j)) * factorY;
}
}
}
void writeResult(Solver* solver)
{
int imax = solver->imax;
int jmax = solver->jmax;
double dx = solver->dx;
double dy = solver->dy;
double* p = solver->p;
double* u = solver->u;
double* v = solver->v;
double x = 0.0, y = 0.0;
FILE* fp;
fp = fopen("pressure.dat", "w");
if (fp == NULL) {
printf("Error!\n");
exit(EXIT_FAILURE);
}
for (int j = 1; j < jmax + 1; j++) {
y = (double)(j - 0.5) * dy;
for (int i = 1; i < imax + 1; i++) {
x = (double)(i - 0.5) * dx;
fprintf(fp, "%.2f %.2f %f\n", x, y, P(i, j));
}
fprintf(fp, "\n");
}
fclose(fp);
fp = fopen("velocity.dat", "w");
if (fp == NULL) {
printf("Error!\n");
exit(EXIT_FAILURE);
}
for (int j = 1; j < jmax + 1; j++) {
y = dy * (j - 0.5);
for (int i = 1; i < imax + 1; i++) {
x = dx * (i - 0.5);
double vel_u = (U(i, j) + U(i - 1, j)) / 2.0;
double vel_v = (V(i, j) + V(i, j - 1)) / 2.0;
double len = sqrt((vel_u * vel_u) + (vel_v * vel_v));
fprintf(fp, "%.2f %.2f %f %f %f\n", x, y, vel_u, vel_v, len);
}
}
fclose(fp);
}

38
BasicSolver/2D-seq/src/solver.h
View File

@@ -6,41 +6,21 @@
*/
#ifndef __SOLVER_H_
#define __SOLVER_H_
#include "discretization.h"
#include "grid.h"
#include "parameter.h"
enum BC { NOSLIP = 1, SLIP, OUTFLOW, PERIODIC };
typedef struct {
/* geometry and grid information */
double dx, dy;
int imax, jmax;
double xlength, ylength;
/* arrays */
double *p, *rhs;
double *f, *g;
double *u, *v;
Grid* grid;
/* parameters */
double eps, omega;
double re, tau, gamma;
double gx, gy;
/* time stepping */
double eps, omega, rho;
int itermax;
double dt, te;
double dtBound;
char* problem;
int bcLeft, bcRight, bcBottom, bcTop;
int levels;
double **r, **e;
} Solver;
extern void initSolver(Solver*, Parameter*);
extern void computeRHS(Solver*);
extern void solve(Solver*);
extern void solveRB(Solver*);
extern void solveRBA(Solver*);
extern void normalizePressure(Solver*);
extern void computeTimestep(Solver*);
extern void setBoundaryConditions(Solver*);
extern void setSpecialBoundaryCondition(Solver*);
extern void computeFG(Solver*);
extern void adaptUV(Solver*);
extern void writeResult(Solver*);
extern void initSolver(Solver*, Discretization*, Parameter*);
extern void solve(Solver*, double*, double*);
#endif

12
BasicSolver/2D-seq/src/util.h
View File

@@ -19,11 +19,11 @@
#define ABS(a) ((a) >= 0 ? (a) : -(a))
#endif
#define P(i, j) p[(j) * (imaxLocal + 2) + (i)]
#define F(i, j) f[(j) * (imaxLocal + 2) + (i)]
#define G(i, j) g[(j) * (imaxLocal + 2) + (i)]
#define U(i, j) u[(j) * (imaxLocal + 2) + (i)]
#define V(i, j) v[(j) * (imaxLocal + 2) + (i)]
#define RHS(i, j) rhs[(j) * (imaxLocal + 2) + (i)]
#define P(i, j) p[(j) * (imax + 2) + (i)]
#define F(i, j) f[(j) * (imax + 2) + (i)]
#define G(i, j) g[(j) * (imax + 2) + (i)]
#define U(i, j) u[(j) * (imax + 2) + (i)]
#define V(i, j) v[(j) * (imax + 2) + (i)]
#define RHS(i, j) rhs[(j) * (imax + 2) + (i)]
#endif // __UTIL_H_