Ctc_3BCid on a degenerated IntervalVector

[NuwanHerathM]

The contractor Ctc_3BCid does not behave as expected when it contracts a degenerated IntervalVector.

/* contractors for the unit disk: x^2 + y^2 <= 1 */
Function f("x","y","x^2 + y^2 - 1");
Interval interval(NEG_INFINITY,0);
CtcFwdBwd c_fwdbwd(f,interval);
Ctc3BCid c_3bcid(c_fwdbwd);

/* box degenerated to the point (-5,0) */
double _x[2]={-5,0};
Vector x(2,_x);
IntervalVector box(x);


/* contraction of the box */
c_3bcid.contract(box);

/* display (-5,0) instead of empty vector */
cout << "Result of the contraction with Ctc3BCid composed with CtcFwdBwd:" << endl;
cout << '\t' << box << endl;

Calling c_fwdbwd.contract(box) instead of c_3bcid.contract(box) actually returns an empty vector.

[gchabert]

This is because, by default, 3BCID does not contract boxes with very small diameters; there are good reasons for that (you should have read the comments of 3BCID, where it is well documented).

To force 3BCID to contract any box, just replace in your code:

Ctc3BCid c_3bcid(c_fwdbwd);

by

Ctc3BCid c_3bcid(c_fwdbwd, Ctc3BCid::default_s3b, Ctc3BCid::default_scid, -1, 0)

and you will get an empty box as expected.