How to interpolate a closed curve

Rhino Developer
1

how to interpolate a closed curve ?
I try like this:
first using rhinointerpcurve creat a curve,
and then using rhinomakecurveclosed make this curve closed
but the closed curve will not smoth at the start and end point.

2

One optional argument for the CreateInterpolatedCurve method is CurveKnotStyle, choosing a “periodic” style should close the curve smoothly.

0 Uniform	 Parameter spacing between consecutive knots is 1.0.
1 Chord  Chord length spacing, requires degree=3 with CV1 and CVn1 specified.
2 ChordSquareRoot	  Square root of chord length, requires degree=3 with CV1 and CVn1 specified.
3 UniformPeriodic  Periodic with uniform spacing.
4 ChordPeriodic  Periodic with chord length spacing.
5 ChordSquareRootPeriodic  Periodic with square roor of chord length spacing.

–Mitch