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wavefield.c
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203 lines (171 loc) · 6.47 KB
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#include <stdlib.h>
#include <math.h>
#include "wavefield.h"
wavefield * wavefield__create(size_t nx, size_t nz) {
wavefield *w = malloc(sizeof (wavefield));
w->nx = nx;
w->nz = nz;
w->grid = calloc(nx * nz, sizeof (double));
w->grid_o = calloc(nx * nz, sizeof (double));
return w;
}
void wavefield__destroy(wavefield *w)
{
free(w->grid);
free(w->grid_o);
free(w);
}
laplacian_params * wavefield__laplacian_params_(double dx, double dz, size_t order, double dt)
{
laplacian_params * lp = malloc(sizeof (laplacian_params));
// Finite Difference Coefficients - Second Derivative - nth order
// TODO: Find algorithimicaly
switch(order) {
case 2:
lp->coef_len = 2;
lp->coef = malloc(lp->coef_len * sizeof(double));
lp->coef[0] = -2.;
lp->coef[1] = 1.;
break;
case 4:
lp->coef_len = 3;
lp->coef = malloc(lp->coef_len * sizeof(double));
lp->coef[0] = -5./2;
lp->coef[1] = 4./3.;
lp->coef[2] = -1./12;
break;
case 6:
lp->coef_len = 4;
lp->coef = malloc(lp->coef_len * sizeof(double));
lp->coef[0] = -49.18;
lp->coef[1] = 3./2;
lp->coef[2] = -3./20;
lp->coef[3] = 1./90;
break;
case 8:
lp->coef_len = 5;
lp->coef = malloc(lp->coef_len * sizeof(double));
lp->coef[0] = -205./72;
lp->coef[1] = 8./5;
lp->coef[2] = -1./5;
lp->coef[3] = 8./315;
lp->coef[4] = -1./560;
break;
}
lp->order = order;
lp->border_size = lp->coef_len - 1; // Size of border depends on stencil
lp->dt = dt;
lp->dt_dx = lp->dt/dx;
lp->dt_dz = lp->dt/dz;
lp->dxdx = dx * dx; // Change in x squared
lp->dzdz = dz * dz; // Change in z squared
lp->coef_dx2 = malloc(lp->coef_len * sizeof(double));
lp->coef_dz2 = malloc(lp->coef_len * sizeof(double));
for(size_t i=0; i < lp->coef_len; i++) {
lp->coef_dx2[i] = lp->coef[i]/lp->dxdx;
lp->coef_dz2[i] = lp->coef[i]/lp->dzdz;
}
return lp;
}
laplacian_params * wavefield__laplacian_params(velocity_model *m, size_t order, double dt)
{
return wavefield__laplacian_params_(m->dx, m->dz, order, dt);
}
void wavefield__destroy_laplacian_params(laplacian_params *lp)
{
free(lp->coef_dx2);
free(lp->coef_dz2);
free(lp->coef);
free(lp);
}
void wavefield__laplacian(wavefield *wave, velocity_model *model, laplacian_params *lp)
{
size_t pos; // Position on flattened grid
double lapx; // Calculated laplacian X axis
double lapz; // Calculated laplacian Z axis
double vel_dt2; // (vel/dt)^2
for(size_t iz = lp->border_size; iz < (model->nz - lp->border_size); iz++) {
for(size_t ix = lp->border_size; ix < (model->nx - lp->border_size); ix++) {
// Position being iterated over in the flatenned array
pos = wave->nx * iz + ix;
// Calculate (vel/dt)^2 in given position
vel_dt2 = powf(model->vel[pos] * lp->dt, 2);
// Stencil center
lapx = lp->coef_dx2[0] * wave->grid_o[pos];
lapz = lp->coef_dz2[0] * wave->grid_o[pos];
// Stencil borders
for(size_t ic=1; ic < lp->coef_len; ic++) {
//x direction
lapx += lp->coef_dx2[ic] * (
wave->grid_o[pos-ic] +
wave->grid_o[pos+ic]);
// Z direction
lapz += lp->coef_dz2[ic] * (
wave->grid_o[pos - (ic * wave->nx)] +
wave->grid_o[pos + (ic * wave->nx)]);
}
// Second order timestep
wave->grid[pos] = 2*wave->grid_o[pos] - wave->grid[pos] + vel_dt2 * (lapx + lapz);
/* **************************************************************
*
* DEBUG PURPOSES
* It will plot the stencil around the area of signal injection
*
***************************************************************/
// size_t mid = 125751;
// if(pos == mid)
// {
// int off = (lp->coef_len-1)/2;
// //fprintf(stderr, "coeflen %zu off: %d\n", lp->coef_len, off);
// for(int i=-off; i <= off ; i++) {
// for(int j=-off; j <= off; j++)
// fprintf(stderr, "(%6zu)%12.8lf ", pos + (i*model->nx) + j, wave->grid[pos+(i*model->nx) +j]);
// fprintf(stderr,"\n");
// }
// fprintf(stderr, "lap_x %14.10lf lap_z %14.10lf vel_dt2 %14.10lf vel %14.10lf\n\n", lapx, lapz, vel_dt2, model->vel[pos]);
// }
// END DEBUG
}
}
}
void wavefield__perfect_match_layer(wavefield *wave, velocity_model *model, laplacian_params *lp)
{
size_t pos;
// Left
for(size_t iz = 0; iz < wave->nz; iz++) {
for(size_t ix = 0; ix < lp->border_size; ix++) {
pos = wave->nx * iz + ix;
wave->grid_o[pos] = wave->grid[pos] +
model->vel[pos] * lp->dt_dx * (wave->grid[pos+1] - wave->grid[pos]);
}
}
// Right
for(size_t iz = 0; iz < wave->nz; iz++) {
for(size_t ix = (wave->nx - lp->border_size); ix < wave->nx; ix++) {
pos = wave->nx * iz + ix;
wave->grid_o[pos] = wave->grid[pos] -
model->vel[pos] * lp->dt_dx * (wave->grid[pos] - wave->grid[pos-1]);
}
}
// Bottom
for(size_t iz = (wave->nz - lp->border_size); iz < wave->nz; iz++) {
for(size_t ix = 0; ix < wave->nx; ix++) {
pos = wave->nx * iz + ix;
wave->grid_o[pos] = wave->grid[pos] -
model->vel[pos] * lp->dt_dx * (wave->grid[pos] - wave->grid[pos-model->nx]);
}
}
// DEBUG IF NEEDED
// fprintf(stderr, "o[%zu]: %lf + v[%zu]: %lf * dt/dx %lf * (o[%zu] %lf - o[%zu] %lf)\n",
// pos, wave->grid_o[pos],
// pos, model->vel[pos], lp->dt_dx,
// pos+1, wave->grid_o[pos+1],
// pos, wave->grid_o[pos]);
}
void wavefield__swap(wavefield *wave)
{
double *tmp;
tmp = wave->grid_o;
wave->grid_o = wave->grid;
wave->grid = tmp;
}