SUBROUTINE echo_f77_setInitialConditions(c, P1, P2, P3, N)
      INTEGER N
      REAL c(N,N), P1(N,N), P2(N,N), P3(N,N)

      INTEGER i, j, blockLeft, blockRight, blockTop, blockBottom
      INTEGER channelLeft, channelRight, channel1Height, channel2Height
      INTEGER cr, cc
      REAL s2

!     Default velocity in the air

      DO j=1,N
        DO i=1,N
          c(i,j) = 0.2;
        END DO
      END DO
    
!     Solid block with which the pulse collids
 
      blockLeft = 1
      blockRight = 2 * N / 5.0
      blockTop = N / 3.0
      blockBottom = 2 * N / 3.0

      DO j=blockLeft,blockRight
        DO i=blockTop,blockBottom
          c(i,j) = 0.5
        END DO
      END DO

!     Channel directing the pulse leftwards

      channelLeft = 4 * N / 5.0
      channelRight = N
      channel1Height = 3 * N / 8.0
      channel2Height = 5 * N / 8.0

      DO j = channelLeft,channelRight
        c(channel1Height,j) = 0.0;
        c(channel2Height,j) = 0.0;
      END DO

!     Initial pressure distribution: a gaussian pulse inside the channel

      cr = N / 2
      cc = 7 * N / 8.0
      s2 = 64.0 * 9.0 / ((N/2.0) ** 2)

      DO j=1,N
        DO i=1,N
          P1(i,j) = 0.0
          P2(i,j) = exp(-((i-cr)**2 + (j-cc)**2) * s2);
          P3(i,j) = 0.0
        END DO
      END DO

      RETURN
      END