Initializing help system before first use

RELAXTREEMEMORYLIMIT

Description
When the memory used by the branch and bound search tree exceeds the target specified by the TREEMEMORYLIMIT control, the optimizer will try to reduce this by writing nodes to the tree file. In rare cases, usually where the solve has many millions of very small nodes, the tree structural data (which cannot be written to the tree file) will grow large enough to approach or exceed the tree's memory target. When this happens, optimizer performance can degrade greatly as the solver makes heavy use of the tree file in preference to memory. To prevent this, the solver will automatically relax the tree memory limit when it detects this case; the RELAXTREEMEMORYLIMIT control specifies the proportion of the previous memory limit by which to relax it. Set RELAXTREEMEMORYLIMIT to 0.0 to force the Xpress Optimizer to never relax the tree memory limit in this way.
Type
Double
Topic areas
Limits, Memory
Default value
0.1
Note
While setting higher values of RELAXTREEMEMORYLIMIT can improve performance significantly for a small number of models in low memory situations, the user is advised to use the TREEMEMORYLIMIT control to tune the memory usage of the branch and bound tree, according to the solve characteristics of their problem, rather than increasing RELAXTREEMEMORYLIMIT.
Affects routines
XPRSmipoptimize ( MIPOPTIMIZE).
See also
TREEMEMORYLIMIT.
Category
Control

Parent Topic Control Parameters

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