PK_ERROR_code_t PK_BSURF_add_u_knot
(
--- received arguments ---
PK_BSURF_t      bsurf,      --- bsurf
double          u           --- U split parameter

--- returned arguments ---
)


This modifies the given bsurf by inserting a knot at the given u split
parameter.


Specific Errors:
    PK_ERROR_is_attached            bsurf is attached to geometry
    PK_ERROR_bad_parameter          bad U parameter given
    PK_ERROR_bad_knots              invalid knot multiplicity


This function modifies a B-surface by inserting a U knot, resulting in
the addition of a row of patches.
The shape of the B-surface is not changed.

The parameter u at which the new knot is to be inserted must be within the
range as given by PK_SURF_ask_params.

The new knot must not increase the multiplicity of any existing knot to more
than the order for an end knot, or order-1 for an internal knot.

If u lies within a patch then a new row of patches will be added to the
surface.

If u lies on a patch boundary then the row of patches added will be null.
Adding a null segment to a surface only affects the B-spline
representation (it duplicates a knot).


A B-surface cannot be modified if it is attached to a face.