4
$\begingroup$

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.

$\endgroup$
  • $\begingroup$ If I remember correctly, .sol files look like xml. Then, if no other way around it, you can use packages in python to read those xml files. Although, I personally just iterate over the solution_value of the variables that I want rather than relying on .sol. Just a thought in case you can do the same. $\endgroup$ – EhsanK Mar 30 at 15:36
6
$\begingroup$

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

| improve this answer | |
$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.