johntfoster / bspline Goto Github PK

Hello John, thanks for this little python module, and sorry if this finds you having forgotten all about it.

I am investigating using this module to implement b-splines rather than reinventing the wheel and I am encountering boundary behavior I don't expect. Given an instantiation of the class

knot_vector = [0, 0, 0, 0, 25, 35, 55, 65, 85, 85, 85, 85]
basis = Bspline(knot_vector,3)
basis.plot()

The final spline as x --> 85 approaches one. However, the value at 85 is zero. Is this expected? My understanding was that this value should actually be equal to one at the final spline

print(basis(84.999))
>>> [  0.00000000e+00   0.00000000e+00   0.00000000e+00   0.00000000e+00
3.33333333e-14   4.99982778e-09   1.49987500e-04   9.99850007e-01]
print(basis(85))
>>> [ 0.  0.  0.  0.  0.  0.  0.  0.]

This is Python 3.5. Thanks for any insight

Hi, thanks for the great repo, can I obtain the derivative of a spline curve f(x)? For example f(x) = sin(x), how can I obtain the f'(x)=cos(x) by the provided API, thank you in advance!

Hi Johnt,
we are using your B-spline package in the framework of tackling parabolic differential equations.
Creating a spline matrix A using ‘collmat’ we find that the last entry (A_nn) is, just like the entire last row 0. Is this a bug? We expected the entire row to be 0, except for the A_nn element, which should be 1. (Just like the A_00 element is 1 and the rest of the A_0-row is 0). Right now we do some ‘artificial fixing’, i.e. setting A_nn to 1 manually.
The problem is also present in the 1st order derivative.