Here is the summary to my question: I have used geoeas until now, which uses a limited number of models. However, I found a program, CurveExpert (AVAILABLE AT http://www.ebicom.net/~dhyams/cvxpt.htm), which finds the best fitting model, which is usually different from the options in geoeas. For example, for my data, I foundthat the best fitting models were a 4th level polynomial model and a "Hoerl" model. Is there any program (downloadable if possible) that would krige with a custom model? Thanks, Carolina
Pierre Goovaerts, Donald E. Myers and Isobel Clark answered You can not fit any type of curve to your experimental variograms since the model needs to be permissible, hence the practice to fit only a limited number of models that are known to be permissible. Pierre Our software, EcoSSe, is enormously flexible and could easily be modified to take a generic model, but it does cost US1,000 When you fit a model you might want to consider a Cressie-like statistics which weights inversely by the model value (or distance) and directly by the number of pairs. Isobel A 4th level polynomial can not be a valid variogram/covariance or even a generalized covariance, consequently you would not want a geostatistics package that would allow the use of such a "model". The problem is that in general the the kriging system would not have a unique solution (in fact might not have a solution at all). While there are more possible valid models (some of which can be obtained by "nesting" the basic models in GeoEas, it is not entirely clear that this would improve the results. To be a valid covariance function, it must be positive definite (as a function). In particular this implies that the function is bounded (hence no polynomials) To be a valid variogram, it must be conditionally negative definite and have a growth rate that is less than quadratic. Donald E. Myers -- * To post a message to the list, send it to [EMAIL PROTECTED] * As a general service to the users, please remember to post a summary of any useful responses to your questions. * To unsubscribe, send an email to [EMAIL PROTECTED] with no subject and "unsubscribe ai-geostats" followed by "end" on the next line in the message body. DO NOT SEND Subscribe/Unsubscribe requests to the list * Support to the list is provided at http://www.ai-geostats.org
