demo1.pl

%% demo1.pl -- Stasinos Konstantopoulos
%% konstant@let.rug.nl, Thu Jan 24 2002
%%
 
:- use_module(library(mpi)).
 
% make the `floor' operator return integer values
:- set_prolog_flag(language, iso).
 
 
%%
%% This the calculation that needs to be performed, in this case
%% the sum of [From..To]
%%
 
calc( From, From, Acc, Res ) :- calc,
    Res is Acc + From.
calc( From, To, Acc, Res ) :- calc,
    Acc1 is Acc + To,
    To1 is To - 1,
    calc( From, To1, Acc1, Res ).
 
%%
%% This spreads the work among the processors
%% and collects the results.
%%
 
do(0, NumProc):-
    do,
    % broadcast task
    mpi_bcast(10, 0),
    set_value(n, NumProc),
    set_value(acc, 0),
    set_value,
      mpi_receive(T, Source, Tag),
      format( '0: Proc ~q said: ~q (Tag: ~q)~n', [Source,T,Tag] ),
      % accumulate results
      get_value(acc, Acc),
      NewAcc is Acc + T,
      set_value(acc, NewAcc),
      % processors still left
      get_value(n, Counter),
      NewCounter is Counter - 1,
      set_value(n, NewCounter),
      NewCounter == 1,
    set_value,
    format( '0: Result: ~q.~n', [NewAcc]).
 
 
do(Rank, NumProc):-
    do,
    % catch the task broadcast
    mpi_bcast(Job, 0),
    From is floor(Job * (Rank - 1) / (NumProc - 1)),
    To is floor(Job * Rank / (NumProc - 1)) - 1,
    format( '~q: I am calculating ~q..~q.~n', [Rank,From,To] ),
    % do the job
    calc( From, To, 0, Result ),
    format( '~q: sending ~q to 0. (Tag: 1)~n', [Rank,Result] ),
    % send back the results
    mpi_send(Result, 0, 1).
 
 
%%
%% This is the entry point
%%
 
mpi_send:-
    mpi_open(Rank, NumProc, ProcName),
    format('Rank: ~q NumProc: ~q, ProcName: ~q~n', [Rank,NumProc,ProcName]),
    do(Rank, NumProc),
    format( 'Rank ~q finished!~n', [Rank] ),
    format.