# ClpSimplexDual Class Reference

This solves LPs using the dual simplex method. More...

`#include <ClpSimplexDual.hpp>`

Inheritance diagram for ClpSimplexDual:
[legend]
Collaboration diagram for ClpSimplexDual:
[legend]

List of all members.

## Public Member Functions
Description of algorithm
int | dual (int ifValuesPass, int startFinishOptions=0)
| Dual algorithm.
int | strongBranching (int numberVariables, const int *variables, double *newLower, double *newUpper, double **outputSolution, int *outputStatus, int *outputIterations, bool stopOnFirstInfeasible=true, bool alwaysFinish=false, int startFinishOptions=0)
| For strong branching.
ClpFactorization * | setupForStrongBranching (char *arrays, int numberRows, int numberColumns, bool solveLp=false)
| This does first part of StrongBranching.
void | cleanupAfterStrongBranching (ClpFactorization *factorization)
| This cleans up after strong branching.
Functions used in dual
int | whileIterating (double *&givenPi, int ifValuesPass)
| This has the flow between re-factorizations Broken out for clarity and will be used by strong branching.
int | updateDualsInDual (CoinIndexedVector *rowArray, CoinIndexedVector *columnArray, CoinIndexedVector *outputArray, double theta, double &objectiveChange, bool fullRecompute)
| The duals are updated by the given arrays.
void | updateDualsInValuesPass (CoinIndexedVector *rowArray, CoinIndexedVector *columnArray, double theta)
| The duals are updated by the given arrays.
void | flipBounds (CoinIndexedVector *rowArray, CoinIndexedVector *columnArray)
| While updateDualsInDual sees what effect is of flip this does actual flipping.
double | dualColumn (CoinIndexedVector *rowArray, CoinIndexedVector *columnArray, CoinIndexedVector *spareArray, CoinIndexedVector *spareArray2, double accpetablePivot, CoinBigIndex *dubiousWeights)
| Row array has row part of pivot row Column array has column part.
int | dualColumn0 (const CoinIndexedVector *rowArray, const CoinIndexedVector *columnArray, CoinIndexedVector *spareArray, double acceptablePivot, double &upperReturn, double &bestReturn, double &badFree)
| Does first bit of dualColumn.
void | checkPossibleValuesMove (CoinIndexedVector *rowArray, CoinIndexedVector *columnArray, double acceptablePivot)
| Row array has row part of pivot row Column array has column part.
void | checkPossibleCleanup (CoinIndexedVector *rowArray, CoinIndexedVector *columnArray, double acceptablePivot)
| Row array has row part of pivot row Column array has column part.
void | doEasyOnesInValuesPass (double *givenReducedCosts)
| This sees if we can move duals in dual values pass.
void | dualRow (int alreadyChosen)
| Chooses dual pivot row Would be faster with separate region to scan and will have this (with square of infeasibility) when steepest For easy problems we can just choose one of the first rows we look at.
int | changeBounds (int initialize, CoinIndexedVector *outputArray, double &changeCost)
| Checks if any fake bounds active - if so returns number and modifies updatedDualBound_ and everything.
bool | changeBound (int iSequence)
| As changeBounds but just changes new bounds for a single variable.
void | originalBound (int iSequence)
| Restores bound to original bound.
int | checkUnbounded (CoinIndexedVector *ray, CoinIndexedVector *spare, double changeCost)
| Checks if tentative optimal actually means unbounded in dual Returns -3 if not, 2 if is unbounded.
void | statusOfProblemInDual (int &lastCleaned, int type, double *givenDjs, ClpDataSave &saveData, int ifValuesPass)
| Refactorizes if necessary Checks if finished.
int | perturb ()
| Perturbs problem (method depends on perturbation()) returns nonzero if should go to dual.
int | fastDual (bool alwaysFinish=false)
| Fast iterations.
int | numberAtFakeBound ()
| Checks number of variables at fake bounds.
int | pivotResultPart1 ()
| Pivot in a variable and choose an outgoing one.
int | nextSuperBasic ()
| Get next free , -1 if none.
int | startupSolve (int ifValuesPass, double *saveDuals, int startFinishOptions)
| Startup part of dual (may be extended to other algorithms) returns 0 if good, 1 if bad.
void | finishSolve (int startFinishOptions)
| This has the flow between re-factorizations Broken out for clarity and will be used by strong branching.
void | gutsOfDual (int ifValuesPass, double *&saveDuals, int initialStatus, ClpDataSave &saveData)
| This has the flow between re-factorizations Broken out for clarity and will be used by strong branching.
void | resetFakeBounds (int type)
| This has the flow between re-factorizations Broken out for clarity and will be used by strong branching.

## Detailed Description

This solves LPs using the dual simplex method.

It inherits from ClpSimplex. It has no data of its own and is never created - only cast from a ClpSimplex object at algorithm time.

Definition at line 23 of file ClpSimplexDual.hpp.

## Member Function Documentation

int ClpSimplexDual::dual | ( | int | ifValuesPass,
|  | int | startFinishOptions = `0` |
| ) |  |  |

Dual algorithm.

Method

It tries to be a single phase approach with a weight of 1.0 being given to getting optimal and a weight of updatedDualBound_ being given to getting dual feasible. In this version I have used the idea that this weight can be thought of as a fake bound. If the distance between the lower and upper bounds on a variable is less than the feasibility weight then we are always better off flipping to other bound to make dual feasible. If the distance is greater then we make up a fake bound updatedDualBound_ away from one bound. If we end up optimal or primal infeasible, we check to see if bounds okay. If so we have finished, if not we increase updatedDualBound_ and continue (after checking if unbounded). I am undecided about free variables - there is coding but I am not sure about it. At present I put them in basis anyway.

The code is designed to take advantage of sparsity so arrays are seldom zeroed out from scratch or gone over in their entirety. The only exception is a full scan to find outgoing variable for Dantzig row choice. For steepest edge we keep an updated list of infeasibilities (actually squares). On easy problems we don't need full scan - just pick first reasonable.

One problem is how to tackle degeneracy and accuracy. At present I am using the modification of costs which I put in OSL and some of what I think is the dual analog of Gill et al. I am still not sure of the exact details.

The flow of dual is three while loops as follows:

while (not finished) {

while (not clean solution) {

Factorize and/or clean up solution by flipping variables so dual feasible. If looks finished check fake dual bounds. Repeat until status is iterating (-1) or finished (0,1,2)

}

while (status==-1) {

Iterate until no pivot in or out or time to re-factorize.

Flow is:

choose pivot row (outgoing variable). if none then we are primal feasible so looks as if done but we need to break and check bounds etc.

Get pivot row in tableau

Choose incoming column. If we don't find one then we look primal infeasible so break and check bounds etc. (Also the pivot tolerance is larger after any iterations so that may be reason)

If we do find incoming column, we may have to adjust costs to keep going forwards (anti-degeneracy). Check pivot will be stable and if unstable throw away iteration and break to re-factorize. If minor error re-factorize after iteration.

Update everything (this may involve flipping variables to stay dual feasible.

}

}

TODO's (or maybe not)

At present we never check we are going forwards. I overdid that in OSL so will try and make a last resort.

Needs partial scan pivot out option.

May need other anti-degeneracy measures, especially if we try and use loose tolerances as a way to solve in fewer iterations.

I like idea of dynamic scaling. This gives opportunity to decouple different implications of scaling for accuracy, iteration count and feasibility tolerance.

for use of exotic parameter startFinishoptions see Clpsimplex.hpp

Reimplemented from ClpSimplex.

int ClpSimplexDual::strongBranching | ( | int | numberVariables,
|  | const int * | variables,
|  | double * | newLower,
|  | double * | newUpper,
|  | double ** | outputSolution,
|  | int * | outputStatus,
|  | int * | outputIterations,
|  | bool | stopOnFirstInfeasible = `true`,
|  | bool | alwaysFinish = `false`,
|  | int | startFinishOptions = `0` |
| ) |  |  |

For strong branching.

On input lower and upper are new bounds while on output they are change in objective function values (>1.0e50 infeasible). Return code is 0 if nothing interesting, -1 if infeasible both ways and +1 if infeasible one way (check values to see which one(s)) Solutions are filled in as well - even down, odd up - also status and number of iterations

Reimplemented from ClpSimplex.

ClpFactorization* ClpSimplexDual::setupForStrongBranching | ( | char * | arrays,
|  | int | numberRows,
|  | int | numberColumns,
|  | bool | solveLp = `false` |
| ) |  |  |

This does first part of StrongBranching.

void ClpSimplexDual::cleanupAfterStrongBranching | ( | ClpFactorization * | factorization | ) |

This cleans up after strong branching.

int ClpSimplexDual::whileIterating | ( | double *& | givenPi,
|  | int | ifValuesPass |
| ) |  |  |

This has the flow between re-factorizations Broken out for clarity and will be used by strong branching.

Reasons to come out: -1 iterations etc -2 inaccuracy -3 slight inaccuracy (and done iterations) +0 looks optimal (might be unbounded - but we will investigate) +1 looks infeasible +3 max iterations

If givenPi not NULL then in values pass

int ClpSimplexDual::updateDualsInDual | ( | CoinIndexedVector * | rowArray,
|  | CoinIndexedVector * | columnArray,
|  | CoinIndexedVector * | outputArray,
|  | double | theta,
|  | double & | objectiveChange,
|  | bool | fullRecompute |
| ) |  |  |

The duals are updated by the given arrays.

Returns number of infeasibilities. After rowArray and columnArray will just have those which have been flipped. Variables may be flipped between bounds to stay dual feasible. The output vector has movement of primal solution (row length array)

void ClpSimplexDual::updateDualsInValuesPass | ( | CoinIndexedVector * | rowArray,
|  | CoinIndexedVector * | columnArray,
|  | double | theta |
| ) |  |  |

The duals are updated by the given arrays.

This is in values pass - so no changes to primal is made

void ClpSimplexDual::flipBounds | ( | CoinIndexedVector * | rowArray,
|  | CoinIndexedVector * | columnArray |
| ) |  |  |

While updateDualsInDual sees what effect is of flip this does actual flipping.

double ClpSimplexDual::dualColumn | ( | CoinIndexedVector * | rowArray,
|  | CoinIndexedVector * | columnArray,
|  | CoinIndexedVector * | spareArray,
|  | CoinIndexedVector * | spareArray2,
|  | double | accpetablePivot,
|  | CoinBigIndex * | dubiousWeights |
| ) |  |  |

Row array has row part of pivot row Column array has column part.

This chooses pivot column. Spare arrays are used to save pivots which will go infeasible We will check for basic so spare array will never overflow. If necessary will modify costs For speed, we may need to go to a bucket approach when many variables are being flipped. Returns best possible pivot value

int ClpSimplexDual::dualColumn0 | ( | const CoinIndexedVector * | rowArray,
|  | const CoinIndexedVector * | columnArray,
|  | CoinIndexedVector * | spareArray,
|  | double | acceptablePivot,
|  | double & | upperReturn,
|  | double & | bestReturn,
|  | double & | badFree |
| ) |  |  |

Does first bit of dualColumn.

void ClpSimplexDual::checkPossibleValuesMove | ( | CoinIndexedVector * | rowArray,
|  | CoinIndexedVector * | columnArray,
|  | double | acceptablePivot |
| ) |  |  |

Row array has row part of pivot row Column array has column part.

This sees what is best thing to do in dual values pass if sequenceIn==sequenceOut can change dual on chosen row and leave variable in basis

void ClpSimplexDual::checkPossibleCleanup | ( | CoinIndexedVector * | rowArray,
|  | CoinIndexedVector * | columnArray,
|  | double | acceptablePivot |
| ) |  |  |

Row array has row part of pivot row Column array has column part.

This sees what is best thing to do in branch and bound cleanup If sequenceIn_ < 0 then can't do anything

void ClpSimplexDual::doEasyOnesInValuesPass | ( | double * | givenReducedCosts | ) |

This sees if we can move duals in dual values pass.

This is done before any pivoting

void ClpSimplexDual::dualRow | ( | int | alreadyChosen | ) |

Chooses dual pivot row Would be faster with separate region to scan and will have this (with square of infeasibility) when steepest For easy problems we can just choose one of the first rows we look at.

If alreadyChosen >=0 then in values pass and that row has been selected

int ClpSimplexDual::changeBounds | ( | int | initialize,
|  | CoinIndexedVector * | outputArray,
|  | double & | changeCost |
| ) |  |  |

Checks if any fake bounds active - if so returns number and modifies updatedDualBound_ and everything.

Free variables will be left as free Returns number of bounds changed if >=0 Returns -1 if not initialize and no effect Fills in changeVector which can be used to see if unbounded and cost of change vector If 2 sets to original (just changed)

bool ClpSimplexDual::changeBound | ( | int | iSequence | ) |

As changeBounds but just changes new bounds for a single variable.

Returns true if change

void ClpSimplexDual::originalBound | ( | int | iSequence | ) |

Restores bound to original bound.

int ClpSimplexDual::checkUnbounded | ( | CoinIndexedVector * | ray,
|  | CoinIndexedVector * | spare,
|  | double | changeCost |
| ) |  |  |

Checks if tentative optimal actually means unbounded in dual Returns -3 if not, 2 if is unbounded.

void ClpSimplexDual::statusOfProblemInDual | ( | int & | lastCleaned,
|  | int | type,
|  | double * | givenDjs,
|  | ClpDataSave & | saveData,
|  | int | ifValuesPass |
| ) |  |  |

Refactorizes if necessary Checks if finished.

Updates status. lastCleaned refers to iteration at which some objective/feasibility cleaning too place.

type - 0 initial so set up save arrays etc

- 1 normal -if good update save

2 restoring from saved

int ClpSimplexDual::perturb | ( |  | ) |

Perturbs problem (method depends on perturbation()) returns nonzero if should go to dual.

int ClpSimplexDual::fastDual | ( | bool | alwaysFinish = `false` | ) |

Fast iterations.

Misses out a lot of initialization. Normally stops on maximum iterations, first re-factorization or tentative optimum. If looks interesting then continues as normal. Returns 0 if finished properly, 1 otherwise.

int ClpSimplexDual::numberAtFakeBound | ( |  | ) |

Checks number of variables at fake bounds.

This is used by fastDual so can exit gracefully before end

int ClpSimplexDual::pivotResultPart1 | ( |  | ) |

Pivot in a variable and choose an outgoing one.

Assumes dual feasible - will not go through a reduced cost. Returns step length in theta Return codes as before but -1 means no acceptable pivot

int ClpSimplexDual::nextSuperBasic | ( |  | ) |

Get next free , -1 if none.

int ClpSimplexDual::startupSolve | ( | int | ifValuesPass,
|  | double * | saveDuals,
|  | int | startFinishOptions |
| ) |  |  |

Startup part of dual (may be extended to other algorithms) returns 0 if good, 1 if bad.

void ClpSimplexDual::finishSolve | ( | int | startFinishOptions | ) |

This has the flow between re-factorizations Broken out for clarity and will be used by strong branching.

Reasons to come out: -1 iterations etc -2 inaccuracy -3 slight inaccuracy (and done iterations) +0 looks optimal (might be unbounded - but we will investigate) +1 looks infeasible +3 max iterations

If givenPi not NULL then in values pass

void ClpSimplexDual::gutsOfDual | ( | int | ifValuesPass,
|  | double *& | saveDuals,
|  | int | initialStatus,
|  | ClpDataSave & | saveData |
| ) |  |  |

This has the flow between re-factorizations Broken out for clarity and will be used by strong branching.

Reasons to come out: -1 iterations etc -2 inaccuracy -3 slight inaccuracy (and done iterations) +0 looks optimal (might be unbounded - but we will investigate) +1 looks infeasible +3 max iterations

If givenPi not NULL then in values pass

void ClpSimplexDual::resetFakeBounds | ( | int | type | ) |

This has the flow between re-factorizations Broken out for clarity and will be used by strong branching.

Reasons to come out: -1 iterations etc -2 inaccuracy -3 slight inaccuracy (and done iterations) +0 looks optimal (might be unbounded - but we will investigate) +1 looks infeasible +3 max iterations

If givenPi not NULL then in values pass

The documentation for this class was generated from the following file:

- /home/coin/svn-release/Alps-1.4.5/Clp/src/ClpSimplexDual.hpp