Hi,

let's go on with the example from https://www.linkedin.com/pulse/what-optimization-how-can-help-you-do-more-less-zoo-buses-fleischer/

 

Warmstart is essential and let's see how we can do that through files with docplex.

 

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.

regards

PS:

Many similar examples at https://www.linkedin.com/pulse/making-optimization-simple-python-alex-fleischer/

 

 

 

 

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