Source code for cylp.py.pivots.PivotPythonBase
'''
This class defines an interface all the Python pivot rules must implement.
It consists of a method :py:func:`pivotColumn` which must be implemented and
:py:func:`isPivotAcceptable` whose implementation is optional.
'''
[docs]class PivotPythonBase:
[docs] def pivotColumn(self):
'''
Every subclass of ``PivotPythonBase``, i.e. every pivot rule, must
implement this method.
Return the index of the entering variable, an integer.
'''
raise NotImplementedError('pivotColumn is not implemented')
[docs] def isPivotAcceptable(self):
'''
This is run just before the actual pivoting happens. Return False
if the pivot is not acceptable for your method.
'''
return True
[docs] def updateReducedCosts(self, updates, spareRow1, spareRow2, spareCol1, spareCol2):
'''
Update the reduced costs as its done in CLP's Dantzig rule.
'''
s = self.clpModel
if updates.nElements:
s.updateColumnTranspose(spareRow2, updates)
s.transposeTimes(-1, updates, spareCol2, spareCol1)
s.reducedCosts[s.nVariables:][updates.indices] -= updates.elements[:updates.nElements]
s.reducedCosts[:s.nVariables][spareCol1.indices] -= spareCol1.elements[:spareCol1.nElements]
updates.clear()
spareCol1.clear()