public override void AddToConstraintSystem(ArrayList /*!*/ /*LinearConstraint*/ clist)
{
//Contract.Requires(clist != null);
// make an unsatisfiable constraint
LinearConstraint lc = new LinearConstraint(LinearConstraint.ConstraintRelation.EQ);
lc.rhs = Rational.FromInt(1);
clist.Add(lc);
}
/// <summary>
/// Applies the Pivot Operation on row "r" and column "c".
///
/// This method can be called when !constructionDone, that is, at a time when not all basis
/// columns have been set up (indicated by -1 in basisColumns). This method helps set up
/// those basis columns.
///
/// The return value is an undo record that can be used with UnPivot.
/// </summary>
/// <param name="r"></param>
/// <param name="c"></param>
public Rational[] /*!*/ Pivot(int r, int c)
{
Contract.Ensures(Contract.Result <Rational[]>() != null);
Contract.Assert(0 <= r && r < rows);
Contract.Assert(0 <= c && c < columns - 1);
Contract.Assert(m[r, c].IsNonZero);
Contract.Assert(inBasis[c] == -1); // follows from invariant and m[r,c] != 0
Contract.Assert(basisColumns[r] != rhsColumn); // follows from invariant and m[r,c] != 0
Rational[] undo = new Rational[rows + 1];
for (int i = 0; i < rows; i++)
{
undo[i] = m[i, c];
}
// scale the pivot row
Rational q = m[r, c];
if (q != Rational.ONE)
{
for (int j = 0; j < columns; j++)
{
m[r, j] /= q;
}
}
// subtract a multiple of the pivot row from all other rows
for (int i = 0; i < rows; i++)
{
if (i != r)
{
q = m[i, c];
if (q.IsNonZero)
{
for (int j = 0; j < columns; j++)
{
m[i, j] -= q * m[r, j];
}
}
}
}
// update basis information
int prevCol = basisColumns[r];
undo[rows] = Rational.FromInt(prevCol);
basisColumns[r] = c;
if (prevCol != -1)
{
inBasis[prevCol] = -1;
}
inBasis[c] = r;
return(undo);
}
