If you do not change the range, but you change your variogram sill (without nugget) the estimation do not change, but change the estimation variance, which is one of the important advantage of kriging. That is not the case for simulations, the variation along mean (in this case SK or, in some cases, OK of the Gaussian values or functions, in the Gaussian framework) depend on kriging standard deviations (converge to this value). Variation in the transformed row values depends also in shape of gaussian anamorfosis function (see the non linear technique confidence interval from anamorfosis function) If the variogram is not Gaussian or cubic (no variance in the origin, infinite integrable) when you put a nugget differences in Kriging estimation are minimum. In the case of such variograms it is necessary to put a little bit of nugget to get stability in estimations, the differences in krigin variance are minimum. Notice that nugget is a discontinuity at the origing, then, the smooth of kriging eliminate the influence of nugget in estimations. Nugget in this case only change sill and then, krigin variance (see some good examples in H. Wakernagels book) In simulation nugget has a notable influence, in dependence of the magnitude. I hope this can help you, If you have another question Ill be happy to give you an answer.
best regards Dr. Adrian Martínez Vargas Revista de Minería y Geología (Editor principal) Departamento de Geología ISMM, Las Coloradas s/n Moa, Holguín Cuba CP 83329 -----Original Message----- From: LUIS ARCIA <[EMAIL PROTECTED]> To: [email protected] Date: Wed, 6 Jun 2007 13:05:48 -0400 Subject: AI-GEOSTATS: The effect of raising and lowering the sill and the absence or presence of a nugget. Dear list: I have some doubt about sill and nugget that I want to share with you to help to clarify it: 1) What is the effect of raising and lowering the sill and the absence or presence of a nugget. For example, let's say I'm going to Krig porosity. If the true variance of the porosity data is 15, what happens to the kriged map if I make the sill value 30? what happen if I make it 5?, What happens to the map If I have a nugget of for example 25%?. 2) Instead of Kriging, let's say I'm doing a conditional simulation of porosity. what are the effects raising and lowering the sill (as above) and adding a nugget (as above)? I'll apreciate all your support and cooperation.. with all my respect to you Luis Arcia PDVSA + + To post a message to the list, send it to [email protected] + To unsubscribe, send email to majordomo@ jrc.it with no subject and "unsubscribe ai-geostats" in the message body. DO NOT SEND Subscribe/Unsubscribe requests to the list + As a general service to list users, please remember to post a summary of any useful responses to your questions. + Support to the forum can be found at http://www.ai-geostats.org/
