Excessive copies of set elements in GMPL

[Domingo Alvarez Duarte]

Hello !

Trying to improve GLPK/GMPL I can see that GMPL model generation is 
making an excessive number of set element copies (see bellow).

For simplicity we declare a SET of 1,000,000 elements and print it's 
cardinality, the profiler show that 3 copies of the set are made, with 
problems with significant size this adds up quickly making then 
unmanageable.

Does someone with more knowledge of the GMPL implementation shed a light 
here ?

It seems that this is a hanging fruit that can give a performance boost 
and reduce the memory usage to 1/3.

See this example:

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set S := {1..1000000};
display card(S);
end;

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Compiling glpk/glpsol for profiling:

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CFLAGS="-g -pg" ./configure

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Then executing:

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glpsol -m test.mod

gprof glpsol gmon.out > glpsol.profile.txt

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Here is the relevant part of the generated profile from gprof:

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Flat profile:

Each sample counts as 0.01 seconds.
  %   cumulative   self              self     total
 time   seconds   seconds    calls  ms/call  ms/call  name
 17.95      0.07     0.07 13000025     0.00     0.00 _glp_dmp_get_atom
  7.69      0.15     0.03  5000000     0.00     0.00 _glp_mpl_copy_symbol
  7.69      0.18     0.03  4000001     0.00     0.00 _glp_mpl_add_member
  7.69      0.21     0.03  1000001     0.00     0.00 _glp_mpl_expand_tuple
  5.13      0.23     0.02 13000008     0.00     0.00 _glp_dmp_free_atom
  5.13      0.25     0.02  4000004     0.00     0.00 _glp_mpl_delete_tuple
  5.13      0.27     0.02  3000001     0.00     0.00 _glp_mpl_arelset_size
  5.13      0.29     0.02  1000001     0.00     0.00 loop_domain_func
  2.56      0.31     0.01  8000003     0.00     0.00 _glp_mpl_tuple_dimen
  2.56      0.33     0.01  3000001     0.00     0.00 _glp_mpl_copy_tuple
  2.56      0.34     0.01  2000000     0.00     0.00 
_glp_mpl_arelset_member
  2.56      0.35     0.01  1000000     0.00     0.00 
_glp_mpl_enter_domain_block
  2.56      0.36     0.01  1000000     0.00     0.00 
_glp_mpl_get_domain_tuple
  2.56      0.37     0.01  1000000     0.00     0.00 _glp_mpl_is_member
  2.56      0.38     0.01  1000000     0.00     0.00 iter_set_func
  2.56      0.39     0.01        3     3.33    44.28 _glp_mpl_copy_elemset
  0.00      0.39     0.00  5000001     0.00     0.00 _glp_mpl_delete_symbol
  0.00      0.39     0.00  4000000     0.00     0.00 _glp_mpl_add_tuple
  0.00      0.39     0.00  2000003     0.00     0.00 _glp_mpl_eval_numeric
  0.00      0.39     0.00  2000000     0.00     0.00 
_glp_mpl_update_dummy_indices
  0.00      0.39     0.00  1000003     0.00     0.00 _glp_mpl_create_tuple
  0.00      0.39     0.00  1000000     0.00     0.00 
_glp_mpl_assign_dummy_index
  0.00      0.39     0.00   999999     0.00     0.00 
_glp_mpl_compare_symbols

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Cheers !