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greg |
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/* Copyright (c) 1991 Regents of the University of California */
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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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* Basic linear regression calculation.
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*/
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#include "linregr.h"
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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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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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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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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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}
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