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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 (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 (

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


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