HiGHS has comprehensive tools for defining and extracting models. This can be done either to/from MPS or (CPLEX) format LP files, or via method calls. HiGHS also has methods that permit the incumbent model to be modified. Solutions can be supplied and extracted using either files or method calls.
As well as returning the value of the cost and bounds, these methods also return the number of nonzeros in the corresponding column or row of the constraint matrix. The indices and values of the nonzeros can be obtained using the methods
Specific matrix coefficients obtained using the method
The most immediate model modification is to change the sense of the objective. By default, HiGHS minimizes the model's objective function. The objective sense can be set to minimize (maximize) using changeObjectiveSense.
Model data for can be changed for one column or row by specifying the index of the column or row, together with the new scalar value for the cost or bounds, the specific methods being changeColCost, changeColBounds. The corresponding method for a row is changeRowBounds. Changes for multiple columns or rows are defined by supplying a list of indices, together with arrays of new values, using the methods changeColsCost, changeColsBounds. The corresponding method for a row is changeRowsBounds. An individual matrix coefficient is changed by passing its row index, column index and new value to changeCoeff.
It may be possible for HiGHS to start solving a model using data obtained by solving a related model, or supplied by a user. Whether this is possible depends on the the class of model being solved, the solver to be used, and the modifications (if any) that have been to the incumbent model since it was last solved.
There can be more basic variables then the number of rows in the model. HiGHS will identify a set of basic variables of the correct dimension by making some basic variables nonbasic
There can be fewer basic variables then the number of rows in the model. HiGHS will identify a set of basic variables of the correct dimension by adding basic variables corresponding to slacks.
For nonbasic variables, it is unnecessary to specify whether they are at their lower or upper bound unless they are "boxed" variables.
If a (partial) feasible assignment of the integer variables is known, this can be passed to HiGHS via setSolution. If integer variables are set to integer values, HiGHS will solve the LP with these integer variables fixed (or MIP if the assignment of the integer variables is not complete). If a feasible solution is obtained, it will be used to provide the MIP solver with an initial primal bound when it run to solve for all integer variables.