c
c
c =========================================================
subroutine rp1ad1(maxmx,meqn,mwaves,mbc,mx,ql,qr,maux,
& auxl,auxr,wave,s,amdq,apdq)
c =========================================================
c
c # solve Riemann problems for the 1D advection equation
c # q_t + u(x) * q_x = 0.
c
c -----------------------------------------------------------
c # In advective form, with interface velocities specified in
c # the auxiliary variable
c # aux(i,1) = u-velocity at left edge of cell i
c -----------------------------------------------------------
c
c # On input, ql contains the state vector at the left edge of each cell
c # qr contains the state vector at the right edge of each cell
c # On output, wave contains the waves,
c # s the speeds,
c # amdq the left-going flux difference A^- \Delta q
c # apdq the right-going flux difference A^+ \Delta q
c
c # Note that the i'th Riemann problem has left state qr(i-1,:)
c # and right state ql(i,:)
c # From the basic clawpack routine step1, rp is called with ql = qr = q.
c
c
implicit double precision (a-h,o-z)
dimension ql(1-mbc:maxmx+mbc, meqn)
dimension qr(1-mbc:maxmx+mbc, meqn)
dimension auxl(1-mbc:maxmx+mbc, maux)
dimension auxr(1-mbc:maxmx+mbc, maux)
dimension s(1-mbc:maxmx+mbc, mwaves)
dimension wave(1-mbc:maxmx+mbc, meqn, mwaves)
dimension amdq(1-mbc:maxmx+mbc, meqn)
dimension apdq(1-mbc:maxmx+mbc, meqn)
c
c # Riemann solver returns flux differences
c ------------
common /rpnflx/ mrpnflx
mrpnflx = 0
c
do 30 i=2-mbc,mx+mbc
c
c # Compute the wave and speed
c
u = auxl(i,1)
c
wave(i,1,1) = ql(i,1) - qr(i-1,1)
s(i,1) = u
amdq(i,1) = dmin1(u, 0.d0) * wave(i,1,1)
apdq(i,1) = dmax1(u, 0.d0) * wave(i,1,1)
30 continue
c
return
end