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## [Bug-gsl] Fwd: gsl_fit_mul results are WRONG [ERRATUM]

**From**: |
blavy pierre |

**Subject**: |
[Bug-gsl] Fwd: gsl_fit_mul results are WRONG [ERRATUM] |

**Date**: |
Sun, 29 Jul 2012 18:17:24 +0200 |

**User-agent**: |
Mozilla/5.0 (Windows NT 5.2; WOW64; rv:14.0) Gecko/20120713 Thunderbird/14.0 |

ERRATUM
The results were caused by a badly cleaned .o file.
All applogizes
-------- Message original --------
Sujet: gsl_fit_mul results are WRONG
Date : Sun, 29 Jul 2012 17:02:12 +0200
De : blavy pierre <address@hidden>
Pour : address@hidden
The doc of gsl_fit_mul states that this functions computes the model :
Y = c_1 *X
Therefore, if run with x=1,2,3 and y=100,101,102, it should return
something around c_1 = 50.
But it returns exactly 1. In fact 1 is the result of the gsl_fit_linear
function, computed with a not null intercept.
The bug is explained because your implementation assume that c_1's in
the two following models are equals, which is of course FALSE.
model 1 : y = c_0 + c_1*x (whant gsl_fit_linear computes)
model 2 : y= 0 + c_1*x (whant gsl_fit_mul SHOULD compute, in fact
it computes model 1 and drop c_0).
Can you please fix it, or patch the doc.
--- gsl_fit_mul documentation ---
Function: int gsl_fit_mul (const double * x, const size_t xstride, const
double * y, const size_t ystride, size_t n, double * c1, double * cov11,
double * sumsq)
This function computes the best-fit linear regression coefficient
c1 of the model Y = c_1 X for the datasets (x, y), two vectors of length
n with strides xstride and ystride. The errors on y are assumed unknown
so the variance of the parameter c1 is estimated from the scatter of the
points around the best-fit line and returned via the parameter cov11.
The sum of squares of the residuals from the best-fit line is returned
in sumsq.