 
float dt=  time sampling interval

float fm=20.0  dominant freq of Ricker wavelet

int gxbeg=  xbegining index of receivers, starting from 0

int gzbeg=  zbegining index of receivers, starting from 0

int jgx=1  receiver xaxis jump interval

int jgz=0  receiver zaxis jump interval

int jsx=  source xaxis jump interval

int jsz=0  source zaxis jump interval

int kt=300  output wavefield at time kt

int nb=20  thickness of sponge ABC

int ng=nx  number of receivers

int nt=  number of time steps

int sxbeg=  xbegining index of sources, starting from 0

int szbeg=  zbegining index of sources, starting from 0

