[Symphony] results of parallel computation

[David Pas]

Hello,

we have solved some IP problem on different architectures.
Below are given the results for a single, two, and sixteen
processor machine. We have expected that the parallelization
will decrease the running time, however we noticed that it
_remained_the_same_. Instead the number of analyzed nodes
increased proportionally with the number of employed CPUs.
The parameters were set such to make symphony stop on the
first found feasible solution. Can someone please clarify
how symphony partitions the work?

Does someone have an idea how we could tell symphony to
use the processors to find the solution faster rather than
to explore more nodes. If we run CPLEX on the same problem
on the same hardware than it indeed returns the result
much faster when more processors are used. That's why
we were surprised to see that with symphony there is
no difference.

Further, does anyone know what is the
"Ramp Up Time (TM)" and the "Ramp Up Time (LP)"
and what is the difference between the two?
They both have always the same value.



============= Other Parameter Settings =============

find_first_feasible 1
gap_limit 1.0

****************************************************
* Stopping After Finding First Feasible Solution   *
* Now displaying stats and best solution found...  *
****************************************************



SINGLE CPU:
===========

======================= CP Timing ===========================
   Cut Pool                  0.000
====================== LP/CG Timing =========================
   LP Solution Time          4491.760
   Variable Fixing           0.000
   Pricing                   0.000
   Strong Branching          1542.970
   Separation                2497.400
=================== Parallel Overhead ======================
   Communication         1.570
   Ramp Up Time (TM)     0.006
   Ramp Up Time (LP)     0.006
   Ramp Down Time        0.000
   Idle Time (Node Pack) 0.006
   Idle Time (Nodes)     0.000
   Idle Time (Names)     0.000
   Idle Time (Diving)    0.009
   Idle Time (Cuts)      0.000
   Total User Time              8534.970
   Total Wallclock Time         8569.264

====================== Statistics =========================
Number of created nodes :       225
Number of analyzed nodes:       113
Depth of tree:                  112
Size of the tree:               225
Number of Chains:               1
Number of Diving Halts:         0
Number of cuts in cut pool:     0
Lower Bound in Root:            3504021.331

Current Upper Bound:         3507742.745
Current Lower Bound:         3504024.121
Gap Percentage:              0.11

Solution Found: Node 224, Level 112
Solution Cost: 3507742.745


2 CPUs:
======

======================= CP Timing ===========================
   Cut Pool                  0.000
====================== LP/CG Timing =========================
   LP Solution Time          6552.920
   Variable Fixing           0.000
   Pricing                   0.000
   Strong Branching          2703.080
   Separation                4420.730
=================== Parallel Overhead ======================
   Communication         2.850
   Ramp Up Time (TM)     1958.151
   Ramp Up Time (LP)     1958.217
   Ramp Down Time        0.000
   Idle Time (Node Pack) 0.015
   Idle Time (Nodes)     0.000
   Idle Time (Names)     0.000
   Idle Time (Diving)    0.028
   Idle Time (Cuts)      0.000
   Total User Time              13680.820
   Total Wallclock Time         7857.234

====================== Statistics =========================
Number of created nodes :       399
Number of analyzed nodes:       200
Depth of tree:                  103
Size of the tree:               399
Number of Chains:               2
Number of Diving Halts:         0
Number of cuts in cut pool:     0
Lower Bound in Root:            3504021.331

Current Upper Bound:         3506535.850
Current Lower Bound:         3504044.208
Gap Percentage:              0.07

Solution Found: Node 395, Level 97
Solution Cost: 3506535.850



16 CPUs:
=======

======================= CP Timing ===========================
   Cut Pool                  0.000
====================== LP/CG Timing =========================
   LP Solution Time          30619.620
   Variable Fixing           0.180
   Pricing                   0.000
   Strong Branching          18797.330
   Separation                32774.290
=================== Parallel Overhead ======================
   Communication         21.880
   Ramp Up Time (TM)     32763.929
   Ramp Up Time (LP)     32764.187
   Ramp Down Time        0.000
   Idle Time (Node Pack) 0.618
   Idle Time (Nodes)     0.000
   Idle Time (Names)     0.000
   Idle Time (Diving)    814.878
   Idle Time (Cuts)      0.000
   Total User Time              82214.540
   Total Wallclock Time         7384.543

====================== Statistics =========================
Number of created nodes :       2295
Number of analyzed nodes:       1148
Depth of tree:                  80
Size of the tree:               2295
Number of Chains:               16
Number of Diving Halts:         0
Number of cuts in cut pool:     0
Lower Bound in Root:            3504021.331

Current Upper Bound:         3506568.896
Current Lower Bound:         3504084.831
Gap Percentage:              0.07

Solution Found: Node 2262, Level 72
Solution Cost: 3506568.896


Thank you in advance,
David



----------------------------------------------------------------
This message was sent using IMP, the Internet Messaging Program.