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## [Help-gsl] Constraints for B-spline breakpoints

**From**: |
Hendrik Weisser |

**Subject**: |
[Help-gsl] Constraints for B-spline breakpoints |

**Date**: |
Tue, 13 Oct 2009 14:10:47 +0200 |

**User-agent**: |
Thunderbird 2.0.0.23 (X11/20090817) |

Dear all,

`I'm using the GSL B-spline functions to implement cubic spline
``smoothing. My program is based on the example in the manual
``(http://www.gnu.org/software/gsl/manual/html_node/Example-programs-for-B_002dsplines.html).
`

`I want to allow varying numbers of breakpoints (nbreak) to achieve
``different degrees of smoothing. The minimum nbreak for cubic splines is
``2, but is there a maximum? If I use more than n-2 (where n is the number
``of data points), I get an error from "gsl_multifit_wlinear" when
``computing the spline coefficients:
`gsl: svd.c:236: ERROR: svd of MxN matrix, M<N, is not implemented
For the offending fit matrix, M = n and N = ncoeffs = nbreak+k-2 = nbreak+2.

`Is there a way to use every (distinct location of a) data point as a
``breakpoint (via "gsl_bspline_knots")?
``Would it be possible to have more breakpoints than data points? If so,
``would it make any sense to allow this?
`
Best regards
Hendrik

**[Help-gsl] Constraints for B-spline breakpoints**,
*Hendrik Weisser* **<=**