subroutine bc2(kappa,l,jdim,jmax,ndim,n,x,t,io,task,u) c General information: c Subroutine bc2 enforces a periodic boundary condition at the c right end of a bar. It must be combined with a periodic c boundary condition bc1 at the other end. c Copyright 1996 Leon van Dommelen c Version 1.0 Leon van Dommelen 12/16/96 c Usage information: c Subroutine bc2 can be called in three different ways depending on c the chosen value of parameter task: c 1. task = 0: c This is the standard call. Subroutine bc2 sets the value c of u(jmax,n) equal to u(1,n). Note that this means that c u(1,n) must already have a value. c 2. task = -1: c This is the inquiry call. Subroutine bc2 changes task to 2 to c indicate it is a periodic boundary condition. c 3. Any other value: c If task is positive, subroutine bc2 merely initializes itself c and exits, otherwise it does nothing at all. c Arguments: c Avoid typos implicit none c Input: conduction constant: double precision kappa c Input: length of the bar: double precision l c Input: declared maximum mesh point index in arrays x and u: integer jdim c Input: actual maximum mesh point index: integer jmax c Input: declared maximum time level index in arrays t and u: integer ndim c Input: time level to set in array u: integer n c Input: array of the x-positions of the mesh points. double precision x(0:jdim) c Input: array of the mesh times t: double precision t(0:ndim) c Input: I/O unit of an already open output file or zero: integer io c Subroutine bc2 only writes to this unit if io is positive. c Input/Output: task to perform: integer task c See the usage information above for more information on task. c Input/Output: temperature values: double precision u(0:jdim,0:ndim) c Provided task equals zero, bc2 sets u(jmax,n) equal to c u(1,n), which must be defined. c If task is nonzero, u is ignored. c External variables and info for compiling or changing subroutine bc2: c The following utility routines from ../../../lib/util.f were used: c cwrite(module,text,io,show) writes line "text" to I/O unit c "io" if nonzero, and to the screen if "show" is nonzero. external cwrite c fatal(module,text1,text2,text3) kills the program after a c fatal error, printing the lines "text1", "text2" and "text3". external fatal c Local variables: c An integer to keep track of whether bc2 has been initialized: integer init c Integer code for a periodic boundary conditions: integer period parameter (period=2) c Data statements: data init/0/ c Executable statements: c For task = -1, change task to indicate a periodic boundary condition: if(task.lt.0)then task=period return endif c Ignore other negative tasks: if(task.lt.0)return c Initialization during the first time that bc2 is called: if(init.eq.0)then c Show which subroutine is being initialized: call cwrite('bc2', & 'Initialization of right boundary condition bc2:',io,0) call cwrite('bc2','- periodic boundary '// & 'condition enforcement at the right end;',io,0) call cwrite('bc2', & '- period/bc_2.f Copyright 1996 Leon van Dommelen.',io,0) c All done with the initialization: init=1 endif c Further ignore nonzero tasks: if(task.ne.0)return c Check the sanity of some of the arguments: if(jdim.le.0 .or. ndim.lt.0 .or. & jmax.le.0 .or. n.lt.0 .or. & jmax.gt.jdim .or. n.gt.ndim)call fatal('bc2', & 'Program error: invalid arguments issued to subroutine bc2.', & 'Fix the program code.',' ') if(jmax.lt.2)call fatal('bc2','Periodic '// &'boundary conditions require at least 2 mesh intervals.',' ',' ') c Set the boundary point: u(jmax,n)=u(1,n) goto 900 c Exit: c Jump here when done: 900 return end