PALM program structure

1
PALM program structure

• Marcus Oliver Letzel
• University of Hannover
• LES / PALM - Seminar
• Zingst, Germany, July 2003

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Contents

• Flow chart
• Initialization
• Run-time (detailed)
• Final steps
• Important variables
• Preprocessor directives

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Flow chart

• Main simplifications
• omit optional software packages (dvrp_graphics,
  spectra, particles)
• omit Euler scheme
• omit cloud physics
• Colours
• normal
• job-chains (initial, restart run)
• user-code (? lecture by J. Uhlenbrock, Sat
  9am)
• important, special explanation on separate
  slide

leap_frog
prognostic_equations
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Initialization
5
Run-time 1/2 leap_frog
standard advection
1D topol.
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Run-time 2/2 prognostic_equations
standard advection
prognostic_equations
prognostic_equations_fast
DO inxl,nxr DO jnys,nyn u-component
ENDDOENDDO
DO inxl,nxr DO jnys,nyn u-component
v-component w-component pt q or s
e (TKE) ENDDO ENDDO
DO inxl,nxr DO jnys,nyn v-component
ENDDOENDDO
w pt q or s
DO inxl,nxr DO jnys,nyn e (TKE)
ENDDOENDDO
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Final steps
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Important variables 1/2

• space
• indices i nxl-1...nxr1 j nys-1...nyn1 k
  nzb ...nzt1
• x, y simple variables z two (!) vertical
  arrays (1nzt1) zu(k) ,
  zwdx , dy dzu(k) zu(k)-zu(k-1),
  dzwddx1/dx, ddy ddzu(k)1/dzu(k) , ddzw
• time
• timestep dt_3d (? timestep.f90)
• counters nt_anz nt_anz
  1 simulated_time simulated_time dt_3d

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Important variables 2/2

• prognostic variables, pointers
• u, v, w, pt, e, q (k,j,i)
• each variable has three pointer arrays and three
  target arraysu_m gt u_1 u gt u_2 u_p gt u_3
  ...
• to swap timelevel, only the targets of the
  pointers are changed, e.g.u_m gt u_2 u gt u_3
  u_p gt u_1 ...
• diagnostic variables
• hom (contains, for example, horizontal and domain
  averages)

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Preprocessor directives 1/2

• What are preprocessor directives?
• Preprocessor directives are little instructions
  to the Fortran compiler that allow to explicitly
  exclude certain parts of the source code from
  compilation. (Syntax ? next slide)
• Where does PALM use preprocessor directives?
• Optional software packages Certain parts of the
  source code will only be activated through
  parameters to be set in mrun (dvrp graphics,
  spectra, particle advection).
• Maschine dependencies Maschine architectures
  differ. A good solution on one maschine may be
  slow or may not work on another machine.As a
  portable model, PALM includes solutions for
  various machine types. But only the relevant
  parts of source code are active for a particular
  run.

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Preprocessor directives 2/2

• Syntax (example)
• if defined( __parallel )print,'parallel
  mode'elseprint,'nonparallel mode'endif
• logical "and" logical "or"

• Important machines
• __ibm IBM regatta (HLRN)__lcmuk linux
  cluster (IMUK)__nec NEC vector (Hamburg)
  __t3eb CRAY T3e (Berlin)
• Important variables
• __parallel parallel execution
• Optional software packages
• __dvrp_graphics extra graphics__spectra
  power spectra__particles particle advection

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A kind of summary Key points

• 3 main program phases
• Initialization, Run-time and Final steps
• Main hierarchy palm.f90, leap_frog.f90,
  prognostic_equations.f90
• staggered grid two z-coordinates
• use multiplication with ddx, ddy, ddzu, ddzw
  instead of division
• be aware of pointers
• be aware of preprocessor directives