FUNCTION ROB_CHECKFIT,Y, YFIT, EPS, DEL, SIG, FRACDEV, NGOOD,W,B,\$ BISQUARE_LIMIT=BLIM ;+ ; NAME: ; ROB_CHECKFIT ; PURPOSE: ; Used by ROBUST_... routines to determine the quality of a fit and to ; return biweights. ; CALLING SEQUENCE: ; status = ROB_CHECKFIT( Y, YFIT, EPS, DEL, SIG, FRACDEV, NGOOD, W, B ; BISQUARE_LIMIT = ) ; INPUT: ; Y = the data ; YFIT = the fit to the data ; EPS = the "too small" limit ; DEL = the "close enough" for the fractional median abs. deviations ; RETURNS: ; Integer status. if =1, the fit is considered to have converged ; ; OUTPUTS: ; SIG = robust standard deviation analog ; FRACDEV = the fractional median absolute deviation of the residuals ; NGOOD = the number of input point given non-zero weight in the ; calculation ; W = the bisquare weights of Y ; B = residuals scaled by sigma ; ; OPTIONAL INPUT KEYWORD: ; BISQUARE_LIMIT = allows changing the bisquare weight limit from ; default 6.0 ; PROCEDURES USED: ; ROBUST_SIGMA() ; REVISION HISTORY: ; Written, H.T. Freudenreich, HSTX, 1/94 ;- ISTAT = 0 IF KEYWORD_SET(BLIM) THEN BFAC=BLIM ELSE BFAC=6. DEV = Y-YFIT SIG=ROBUST_SIGMA(DEV,/ZERO) ; If the standard deviation = 0 then we're done: IF SIG LT EPS THEN GOTO,DONE IF DEL GT 0. THEN BEGIN ; If the fraction std. deviation ~ machine precision, we're done: Q=WHERE( ABS(YFIT) GT EPS, COUNT ) IF COUNT LT 3 THEN FRACDEV = 0. ELSE \$ FRACDEV = MEDIAN(ABS( DEV[Q]/YFIT[Q] ),/EVEN ) IF FRACDEV LT DEL THEN GOTO,DONE ENDIF ISTAT = 1 ; Calculate the (bi)weights: B = ABS(DEV)/(BFAC*SIG) S = WHERE( B GT 1.0,COUNT ) & IF COUNT GT 0 THEN B[S] = 1. NGOOD = N_ELEMENTS(Y)-COUNT W=(1.-B^2) W=W/TOTAL(W) DONE: RETURN, ISTAT END