Presolve removed variables

Solvers are pretty clever and usually find spots in the model that are not relevant to the solution. These spots will be removed and therefore the matrix shrinks.

You might want to have a closer look at the solver's work and check if your model or data has a general defect. For example, a group of variables (a VariableCollection) is completely removed: is it really unnecessary? Have constraints been forgotten?

Solver-output as shown in the getting-started example

Presolve removed 22 rows and 12 columns
Presolve time: 0.00s

Get more information

Before creating the ModelScope, the settings have to be configured in order to compute the removed variables.
Insert this configuration into the example.

var scopeSettings = new Configuration()
{
    NameHandling = NameHandlingStyle.UniqueLongNames,
    ComputeRemovedVariables = true;
};

The Statistics will then include a column RemovedInPreprocess in the the export. Just export the Statistics by using:

// Write Statistics to AppDomain.CurrentDomain.BaseDirectory
designModel.Model.VariableStatistics.WriteCSV(AppDomain.CurrentDomain.BaseDirectory);

The Statistics in this case will be:

VariableNameInModel	VariableLongName	LB	UB	SubjectivePrice	SolutionValue	RemovedInPreprocess	NumberOfTermsInRestrictions	Index0
A	Flow Paderborn to New York_A	0.00	Infinity	3.00	100.00	True	4	Edge Paderborn to New York
AQ	Flow Paderborn to São Paulo_AQ	0.00	Infinity	5.00	0.00	True	4	Edge Paderborn to São Paulo
Ag	Flow Beijing to Paderborn_Ag	0.00	50.00	1.00	50.00	True	4	Edge Beijing to Paderborn
Aw	Flow New York to Beijing_Aw	0.00	Infinity	2.00	0.00	True	4	Edge New York to Beijing
B	Flow Beijing to São Paulo_B	0.00	75.00	1.00	0.00	True	4	Edge Beijing to São Paulo
BQ	Flow São Paulo to San Francisco_BQ	0.00	Infinity	4.00	50.00	True	4	Edge São Paulo to San Francisco

Which actually means that this model is so easy to solve, that the solver does all the work in preprocessing and removes all the variables. (Usually just some variables are removed.)

Note: Use any text editor like notepad or similar to view the csv-files. depending on your machine's region-settings, Microsoft Excel will read the file as a worksheet and split the lines into columns.