Yang
Yes the lagrangian multipier is subtracted, assuming you used the
semi-variogram in your kriging equations. If you use the covariance, it is
added.
The extra terms in the back transform are to correct for the difference between
the variance of the true values and the variance of the estimators. If you are
estimating at points, the estimator is a weighted average which will have a
smaller variance than single point values. Back transforming values with a
smaller variance will bias the estimates downwards.
If you want unbiassed estimated values, you have to follow the formula.
Hope this helps
Isobel
http://drisobelclark.kriging.com
--- On Mon, 21/12/09, yang yu fareyouw...@gmail.com wrote:
From: yang yu fareyouw...@gmail.com
Subject: AI-GEOSTATS: Sign of the Lagrange Multiplier Used in Back-transform
To: ai-geostats@jrc.it
Date: Monday, 21 December, 2009, 21:02
Hello all,
I'm trying to apply the lognormal kriging method
to a highly negatively skewed dataset (data were reflected
first). The back_transform formula given in the reference
book takes the following form:
Z(x) = EXP[ EstimatedValue + KrigingVariance/s -
LagrangeMultiplier]
in which the Lagrange multiplier is subtracted from the the
first 2 items. Is this formula assuming that the Lagrange
multiplier value calculated for each block/cell is POSITIVE?
All of the Lagrange values I got for my dataset are
NEGATIVE. In this case, should the negative Lagrange values
be ADDED to the first 2 items?
Many thanks for any guidance and happy hollidays
Regards,
Yang
+
+ To post a message to the list, send it to ai-geost...@jrc.ec.europa.eu
+ To unsubscribe, send email to majordomo@ jrc.ec.europa.eu 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/
