Memory used by AMPL

[Alessandro Oscar Gilardino Arias]

Dear Bob, I have one question.

When I am solving my linear programs in AMPL using CPLEX in the solving process I use cplex_options 'mipdisplay=2 mipinterval=100 lpdisplay=1 bardisplay=1' and each several number of iteration I have the following messages:

       Nodes                                         Cuts/

   Node  Left     Objective  IInf  Best Integer    Best Bound    ItCnt     Gap

      0     0     9702.0000   139                   9702.0000        0         

      0     2     9702.0000    94                   9702.0000        0         

Elapsed time = 20.64 sec. (6099.74 ticks, tree = 0.00 MB)

    100    70    infeasible                         9702.0606   129330         

    200   138     9709.7725    68                   9703.9964   163985         

    300   222    infeasible                         9703.9964   203070         

    400   303     9749.6241    44                   9703.9964   243956         

    500   386     9791.6618    44                   9703.9964   268866         

    600   470     9729.6035    82                   9705.1180   296710         

    700   556     9744.4411    92                   9705.1180   322783         

    800   645     9762.6251    87                   9705.1180   350852         

    900   740     9753.7853    71                   9705.3813   386273         

   1000   839     9845.5933    48                   9705.3813   404430         

Elapsed time = 196.16 sec. (56047.96 ticks, tree = 62.88 MB)

   1100   900     9838.2529    41                   9705.3813   420742         

   1200   961     9714.2390   195                   9706.2679   452034         

   1300  1056     9737.5986    40                   9706.2679   489103         

I would like to know if yout could explain me what means the following   tree = 62.88 MB)

Is that the memory used by AMPL to solver the linear program? If I have 8Gb of RAM memory, that means that tree<= 8Gb?? and what happens if I need more than 8 Gb to solve my model??

Thanks in advance

[Robert Fourer]

CPLEX's solution method builds a search tree of fractional solutions, and "tree = 62.88 MB" tells you that the tree data structure is currently taking up 62.88 megabytes in memory. If the tree gets too big then CPLEX will terminate with an out-of-memory error. However you can deal with this by directing CPLEX to write some of the tree to disk, by setting 'nodefile=2' or 'nodefile=3' as described at http://ampl.com/products/solvers/solvers-we-sell/cplex/options/.

Bob Fourer
am...@googlegroups.com

=======

[Alessandro Oscar Gilardino Arias]

Thank very much Bob, I am using the Cplex_options:

  option cplex_options 'mipdisplay=2 mipinterval=100 lpdisplay=1 bardisplay=1'

I have to add to this to cplex_options like this?

  option cplex_options 'mipdisplay=2 mipinterval=100 lpdisplay=1 bardisplay=1 nodefile=2'?

thanks

[Robert Fourer]

That is right.