Re: Error models and weighting

From: "Niclas Jonsson" <Niclas.Jonsson@farmbio.uu.se> Subject: Re: Error models and weighting Date: Thu, 24 May 2001 09:47:29 +0200 David, I thought two steps ahead and made an erroneous comment about the fixing SIGMA to 1, sorry for that. With the syntax below you should not fix SIGMA to 1. Had the W statement been (THETA(1)*F**2+THETA(2)**2)**0.5 then, with a fixed SIGMA, THETA(1) would be the SD of the prop error and THETA(2) would be the SD ADD error. The valid values for 0 you have will make the code below give you problems. The DEL thing is just protective coding to avoid division by zero. If you omit the W=W+DEL line and say IWRES=IRES/(W+DEL) then only the IWRES will be incorrect for the DV=0 points but the actual fit will not be affected (IWRES is nothing that NM understands, its just for display purposes). Best, Niclas