[SOLVED] How to perform a SGS (seq. gauss. simulation)

If you have problems using RGeostats package or if you simply need some help on an unlisted subject.

[SOLVED] How to perform a SGS (seq. gauss. simulation)

Postby Gustavo Ramos » Mon Nov 23, 2015 7:41 pm

Good afternoon.
I would like to know how to perform a sequential gaussian simulation in RGeostats.
I'm trying to compare the results of a ordinary kriging with the SGS but I can't find how to perform it within the RGeostats package.
Is there a way to do it?
Thanks for the attention.
Gustavo Ramos
 
Posts: 2
Joined: Mon Nov 23, 2015 7:33 pm

Re: How to perform a SGS (sequential gaussian simulation)

Postby Didier Renard » Thu Nov 26, 2015 10:15 am

Sorry to say that there is no SGS simulation in the current version.
I imagine I will have to program it for the next version
Didier Renard
 
Posts: 337
Joined: Thu Sep 20, 2012 4:22 pm

Re: How to perform a SGS (sequential gaussian simulation)

Postby Gustavo Ramos » Thu Nov 26, 2015 10:23 am

Good morning.
Thanks for the help.
Gustavo Ramos
 
Posts: 2
Joined: Mon Nov 23, 2015 7:33 pm

Re: [SOLVED] How to perform a SGS (seq. gauss. simulation)

Postby Jeffrey Yarus » Wed Jul 26, 2023 5:45 pm

Was SGS or SIS ever added to RGeostats?
Jeffrey Yarus
 
Posts: 48
Joined: Wed Jun 26, 2019 9:39 pm

Re: [SOLVED] How to perform a SGS (seq. gauss. simulation)

Postby Didier Renard » Thu Aug 03, 2023 5:55 pm

Hi Jeffrey
Sorry for this late answer. And sorry for this NEGATIVE answer.

Let us recall the main principle of the sequential (conditional) simulation... In turn, we consider a new target. We calculate the estimation at the target site, based on whatever information is available at the current time (i.e. the initial hard data + the values at the target sites processed before the current one). This estimation, to which we add a random term (obtained sampled from a normal distribution but tuned to the variance of the estimation error), produce the conditional simulation at the current target site.
This new simulated value will be part of the available information when processing the next target site.

In RGeostats (and still in future gstlearn), we have not been willing to add the Sequential simulation technique. Essentially for two reasons:
- a theoretical one: Unless we always consider ALL the previously simulated targets in the kriging procedure, the results of such a procedure is unsafe (unless we use specific models and pattern of information where screen effect is valid). Therefore the available information grows with the rank of the target site. This quickly leads to an issue as the kriging system becomes huge and inverting it becomes intractable. Then people usually introduce a problem reduction by introducing a *neighborhood*. The impact of this neighborhood on the quality of the result has not been seriouly analyzed (for my point of view).
- a practical one: at each sequence, the information comes on one hand from the initial data, and from the already simulated targets on the other hand. A proper implementation would require handling a double neighborhood ... which is not available in RGeostats (nor in gstlearn).

Sorry.
Didier Renard
 
Posts: 337
Joined: Thu Sep 20, 2012 4:22 pm

Re: [SOLVED] How to perform a SGS (seq. gauss. simulation)

Postby Jeffrey Yarus » Mon Aug 07, 2023 9:36 pm

Hi Didier: Don't apologize, I don't use SGS or SIS very much, principally for the reasons you state. I was just looking to see if you included it because some students were asking. That said, I continued to be surprised to find that so many people continue to use it...
Jeffrey Yarus
 
Posts: 48
Joined: Wed Jun 26, 2019 9:39 pm


Return to Other Troubleshooting

Who is online

Users browsing this forum: No registered users and 11 guests

cron