*From*: i7tiol t-online de (Olaf Till)*To*: gnumeric-list gnome org*Subject*: Code for 2 new Gnumeric functions (logarithmic regression)*Date*: Tue, 10 Sep 2002 18:45:26 +0200

Hello, This is a request that you consider to incorporate the attached code for two new functions into the Gnumeric distribution. I am no registered Gnumeric developer. If there is a more appropriate place to send this request to, please tell me. I have written this code for Gnumeric version 1.0.9. The functions both perform logarithmic regression. The fitted logarithmic equations can mimic the trend of some types of scientific data and serve as calibration-equations for the calculation of unknowns. 1.) ``LOGREG'' fits the parameters `a' and `b' of the equation "y = b + a * log(x)". It transforms x's to z=log(x) and then calls ``general_linear_regression'' written by others to perform a linear regression of y's and z's. Although the transformation to log(x) could also be done within a worksheet, logarithmic regression seemed general enough to me to deserve an extra function. In Excel, this functionality is not available as a function, but is available as a ``trend curve'' within graphs. ``general_linear_regression'' written by others provides multidimensional regression, although the corresponding ``LINEST'' function is not yet quite ready to deal with more than one independent variable. ``LOGREG'' is prepared to use this functionality, as soon as LINEST uses it, too --- although I do not know if multidimensional regression of logarithmically transformed independent data is useful in statistical praxis. 2.) ``LOGFIT'' fits the parameters `sign', `a', `b', and `c' of the equation "y = a + b * log (sign * (x - c))", with sign in {-1, +1}. This equation can be well adapted to point clouds which, although shaped ``logarithmic'', are shifted in the direction of the x-axis. In these cases, ``LOGREG'' would often fail or produce bad fits. At work, I have often encountered such data in assays which correlate optical densities with substance amounts. If sign == -1, the graph of the equation is mirrored across the y-axis. ``LOGFIT'' performs non-linear fitting. It searches for the best c while computing the corresponding a and b for each c by a simple linear regression. This approach could also be carried out using a general solver, but then the success would depend on the choosing of suitable starting parameters (I have tried it with the Excel solver), and the preparation of such a worksheet would be complicated. A function corresponding to ``LOGFIT'' is not available in Excel. The two functions would affect the files regression.c and regression.h, of which Morten Welinder and Andrew Chatham are the authors, and the file functions/fn-stat.c. ``LOGREG'' relies on code from these authors in these files. Regards, Olaf

**Attachment:
regression.c.1.0.9.diff**

**Attachment:
regression.h.1.0.9.diff**

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fn-stat.c.1.0.9.diff**

**Follow-Ups**:**Re: Code for 2 new Gnumeric functions (logarithmic regression)***From:*Jody Goldberg

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