I've been to trying to read a .sol file in cplex python API before solving the problem but couldn't find any command to do so. There are analogous commands for this operation in c++, c, and Java.
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1 Answer
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First, let us see how to write a .mst file
from docplex.mp.model import Model
mdl = Model(name='buses')
nbbus40 = mdl.integer_var(name='nbBus40')
nbbus30 = mdl.integer_var(name='nbBus30')
mdl.add_constraint(nbbus40*40 + nbbus30*30 >= 300, 'kids')
mdl.minimize(nbbus40*460 + nbbus30*360)
sol=mdl.solve()
for v in mdl.iter_integer_vars():
print(v," = ",v.solution_value)
sol.export_as_mst(path="C:/", basename="file.mst")
generates file.mst
<?xml version = "1.0" standalone="yes"?>
<?xml-stylesheet href="https://www.ilog.com/products/cplex/xmlv1.0/solution.xsl" type="text/xsl"?>
<!-- This file has been generated by DOcplex version 2.4.61 -->
<CPLEXSolution version="1.0">
<header
problemName="buses"
objectiveValue="3480"
/>
<variables>
<variable name="nbBus40" index="0" value="6"/>
<variable name="nbBus30" index="1" value="2"/>
</variables>
</CPLEXSolution>
and then to warm start from there:
from docplex.mp.model import Model
mdl = Model(name='buses')
nbbus40 = mdl.integer_var(name='nbBus40')
nbbus30 = mdl.integer_var(name='nbBus30')
mdl.add_constraint(nbbus40*40 + nbbus30*30 >= 300, 'kids')
mdl.minimize(nbbus40*460 + nbbus30*360)
mdl.get_cplex().MIP_starts.read("c:/file.mst")
sol=mdl.solve(log_output=True)
for v in mdl.iter_integer_vars():
print(v," = ",v.solution_value)
which will display
1 of 1 MIP starts provided solutions.
MIP start 'm1' defined initial solution with objective 3480.0000.
from warmstart here
.solfiles look likexml. Then, if no other way around it, you can use packages in python to read thosexmlfiles. Although, I personally just iterate over thesolution_valueof the variables that I want rather than relying on.sol. Just a thought in case you can do the same. $\endgroup$