Dear Uwe, The interpretation of the nlag parameter in sasim can be somewhat confusing. It corresponds to the number of lags in all directions to be incorporated in the objective functions, not the class of distance for the semivariogram model. For example, to reproduce the variogram for the 1st "lag distance" of 0.5 km in all directions, you need to specify nlags=8, which corresponds to the number of cells in the direct neighborhood of the cell being simulated. For reproducing the 2nd class of distance of 1km, nlags should be 24. So the formula to use to reproduce K classes of distances would be nlag=[(2K+1)^2]-1. So if you want to reproduce the variogram up to a distance of 20 kms using a grid size of 0.5km nlag=[(2x40+1)^2]-1=6560! I have recently looked at ways to sample this set of lags since it is clearly impossible to afford such a large number of lags in the objective function. For example, only a random subset of these 6,560 possible lags would be reproduced. This is a limitation of the simulated annealing algorithm (would be even worst in 3D) and any other suggestions would be much appreciated.
Regards, Pierre Goovaerts <><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><> Dr. Pierre Goovaerts President of PGeostat, LLC Chief Scientist with Biomedware Inc. 710 Ridgemont Lane Ann Arbor, Michigan, 48103-1535, U.S.A. E-mail: [EMAIL PROTECTED] Phone: (734) 668-9900 Fax: (734) 668-7788 http://alumni.engin.umich.edu/~goovaert/ <><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><> On Fri, 13 Jun 2003, Uwe Haberlandt wrote: > Dear all, > > I have a question concerning the simulated annealing module within GSLIB > (f77v2 and f90). I'm using kilometers as units with grid spacing of 0.5 > km and wanted a reproduction of the variogram up to a distance of 20 km. > The range is 10 km. However for different nlags set in the parameter > file (e.g. 20, 40, 80,120) the debugging file reports variogram values > (actual and model) much lower than expected. In the debugging file the > model variogram does not reach the sill not even with nlags=120. How is > "nlags" interpreted and what is reported in the debug file? > > Any help is greatly appreciated > Regards > Uwe > > > ********************************************************** > Dr. Uwe Haberlandt > Ruhr University Bochum > Institute for Hydrology, Water Management > and Environmental Engineering > Universitätsstraße 150 > 44780 Bochum > Germany > Tel.: +49 (0)234-32-27619 > Fax.: +49 (0)234-32-14153 > e-mail: [EMAIL PROTECTED] > www: http://www.ruhr-uni-bochum.de/hydrology/ > ********************************************************** > > -- * 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
