PHOTON USE
  p; parphi;  1 1 500
 
  gr ou y 1
  gr off;red;gr ou y 1
  msg pressure; distance is vertical, time horizontal
  con p1 y 1 fi;1
  msg Press  to continue
  pause
  con off
  red
  msg velocity; distance is vertical, time horizontal
  con u1 y 1 fi;1
  msg trajectory of interface
  con c3 y 1 col 1; 1.1  1.11  2
  enduse
l($321
    GROUP 1. Run title and other preliminaries
TEXT(Shock Tube                         
TITLE
  DISPLAY
  High-pressure air is separated from low-pressure air by a
  diaphragm at the mid-section of a tube with closed ends.
 
  The diaphragm suddenly breaks.
 
  The subsequent motion is predicted by a one-dimensional analysis,
  similar to that of case 321, which is first loaded.
 
  The differences from case 321 are:-
 
  (1) the initial conditions of pressure and velocity; and
  (2) the solution of the "marker" variable C3, which serves as a
      multiplier in the density formula.
 
  ENDDIS
STEADY=F
 
    GROUP 7. Variables stored, solved & named
SOLVE(C3)
TERMS(C3,Y,Y,N,Y,Y,Y)
 
    GROUP 11. Initialization of variable or porosity fields
FIINIT(P1)=REFPRE;FIINIT(U1)=0.0;FIINIT(RHO1)=REFRHO
FIINIT(C3)=1.0
PATCH(START,INIVAL,1,NX/2,1,1,1,1,1,1);INIADD=F
COVAL(START,P1,0.0,REFPRE*2.0)
COVAL(START,RHO1,0.0,REFRHO*2.0)
COVAL(START,C3,0.0,2.0/(2.0**RHO1B))
SPEDAT(SET,GXMONI,TRANSIENT,L,F)