See pppm.h. These sections define the bounds of the regular
3d grid on each proc, and which variables store grid values:
int nxlo_in,nylo_in,nzlo_in,nxhi_in,nyhi_in,nzhi_in;
int nxlo_out,nylo_out,nzlo_out,nxhi_out,nyhi_out,nzhi_out;
int nxlo_ghost,nxhi_ghost,nylo_ghost,nyhi_ghost,nzlo_ghost,nzhi_ghost;
int nxlo_fft,nylo_fft,nzlo_fft,nxhi_fft,nyhi_fft,nzhi_fft;
int nlower,nupper;
int ngrid,nfft,nfft_both;
FFT_SCALAR ***density_brick;
FFT_SCALAR ***vdx_brick,***vdy_brick,***vdz_brick;
FFT_SCALAR ***u_brick;
FFT_SCALAR ***v0_brick,***v1_brick,***v2_brick;
FFT_SCALAR ***v3_brick,***v4_brick,***v5_brick;
double *greensfn;
double **vg;
double *fkx,*fky,*fkz;
FFT_SCALAR *density_fft;
FFT_SCALAR *work1,*work2;
Then find where the grid index variables are defined in the code.
Steve