c     ==================================================================
      subroutine setaux(maxmx,maxmy,maxmz,mbc,mx,my,mz,xlower,ylower,
     &                  zlower,dx,dy,dz,maux,aux)
c     ==================================================================
c
c     # set auxiliary arrays
c
c     # acoustics in a heterogeneous medium:
c     #  aux(i,j,k,1) = impedance Z in (i,j) cell
c     #  aux(i,j,k,2) = sound speed c in (i,j) cell
c
c
      implicit double precision (a-h,o-z)
      double precision aux(1-mbc:maxmx+mbc, 1-mbc:maxmy+mbc,
     &               1-mbc:maxmz+mbc, maux)
      common /comaux/ z1,c1,z2,c2


      do  k = 1-mbc,mz+mbc
	 do j = 1-mbc,my+mbc
	    do i = 1-mbc,mx+mbc
               zcell = zlower + (k-0.5d0)*dz
               if (zcell .lt. 0.d0) then
	          aux(i,j,k,1) = z1
	          aux(i,j,k,2) = c1
                else
	          aux(i,j,k,1) = z2
	          aux(i,j,k,2) = c2
                endif
            enddo
         enddo
      enddo

      return
      end