rp1tr.f.html Source file:   rp1tr.f Directory:   /Users/rjl/git/rjleveque/clawpack-4.6.3/book/chap17/onramp Converted:   Mon Jan 21 2013 at 20:15:36   using clawcode2html This documentation file will not reflect any later changes in the source file.

```
c
c
c =========================================================
subroutine rp1(maxmx,meqn,mwaves,mbc,mx,ql,qr,auxl,auxr,
&		 wave,s,amdq,apdq)
c =========================================================
c
c     # solve Riemann problems for the traffic equation.
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    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)
logical efix
common /comrp/ umax
c
c
efix = .true.   !# Compute correct flux for transonic rarefactions
c
do 30 i=2-mbc,mx+mbc
c
c        # Compute the wave and speed
c
wave(i,1,1) = ql(i,1) - qr(i-1,1)
s(i,1) = umax * (1.d0 - (qr(i-1,1) + ql(i,1)))
c
c
c        # compute left-going and right-going flux differences:
c        ------------------------------------------------------
c
amdq(i,1) = dmin1(s(i,1), 0.d0) * wave(i,1,1)
apdq(i,1) = dmax1(s(i,1), 0.d0) * wave(i,1,1)
c
if (efix) then
c           # entropy fix for transonic rarefactions:
sim1 = umax*(1.d0 - 2.d0*ql(i-1,1))
si = umax*(1.d0 - 2.d0*ql(i,1))
if (sim1.lt.0.d0 .and. si.gt.0.d0) then
flux0 = 0.25d0*umax
fluxim1 = qr(i-1,1)*umax*(1.d0 - qr(i-1,1))
fluxi   = ql(i,1)*umax*(1.d0 - qr(i,1))
amdq(i,1) = flux0 - fluxim1
apdq(i,1) = fluxi - flux0
endif
endif
30   continue
c
return
end
```