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/* Copyright (c) 1991 Regents of the University of California */ |
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|
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#ifndef lint |
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static char SCCSid[] = "$SunId$ LBL"; |
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#endif |
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|
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/* |
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* Basic linear regression calculation. |
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*/ |
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|
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#include <math.h> |
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|
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#include "linregr.h" |
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|
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|
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lrclear(l) /* initialize sum */ |
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register LRSUM *l; |
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{ |
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l->xs = l->ys = l->xxs = l->yys = l->xys = 0.0; |
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l->n = 0; |
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} |
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|
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|
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flrpoint(x, y, l) /* add point (x,y) to sum */ |
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double x, y; |
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register LRSUM *l; |
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{ |
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l->xs += x; |
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l->ys += y; |
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l->xxs += x*x; |
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l->yys += y*y; |
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l->xys += x*y; |
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return(++l->n); |
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} |
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|
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|
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lrfit(r, l) /* compute linear regression */ |
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register LRLIN *r; |
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register LRSUM *l; |
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{ |
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double nxvar, nyvar; |
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|
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if (l->n < 2) |
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return(-1); |
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nxvar = l->xxs - l->xs*l->xs/l->n; |
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nyvar = l->yys - l->ys*l->ys/l->n; |
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if (nxvar == 0.0 || nyvar == 0.0) |
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return(-1); |
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r->slope = (l->xys - l->xs*l->ys/l->n) / nxvar; |
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r->intercept = (l->ys - r->slope*l->xs) / l->n; |
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r->correlation = r->slope*sqrt(nxvar/nyvar); |
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return(0); |
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} |
