[R-sig-Geo] 'LDLfactor' error in 'krige' function

[Mauricio Zambrano]

Dear List,

During some OK interpolations of daily precipitation, with the
'automap' library, I got the following error:


[using ordinary kriging]
"chfactor.c", line 130: singular matrix in function LDLfactor()
Error en predict.gstat(g, newdata = newdata, block = block, nsim = nsim,  :
  LDLfactor


The code I'm using works fine for other days, so I assume that the
distance between the measurement points is no the problem. When
looking at the data that rose the error, I realized that all the
measured values were equal to zero (I can not skip those days in which
all the measured points have the same value in advance, because the
measured value in those points change with time).

According to a traceback that is given below, it seems that the cause
is in the 'predict.gstat' function of the 'gstat' package.

The same error can be risen with:

# Data preparation
data(meuse)
coordinates(meuse) =~ x+y
data(meuse.grid)
gridded(meuse.grid) =~ x+y

meuse$zinc <- meuse$zinc*0
meuse$zinc

# Ordinary kriging, no new_data object
kriging_result = autoKrige(zinc~1, meuse)


traceback()
6: .Call("gstat_predict", as.integer(nrow(as.matrix(new.X))),
as.double(as.vector(raw$locations)),
       as.vector(new.X), as.integer(block.cols), as.vector(block),
       as.vector(bl_weights), as.integer(nsim), as.integer(BLUE))
5: predict.gstat(g, newdata = newdata, block = block, nsim = nsim,
       indicators = indicators, na.action = na.action, debug.level =
debug.level)
4: .local(formula, locations, ...)
3: krige(formula, input_data, new_data, variogram_object$var_model,
       block = block, ...)
2: krige(formula, input_data, new_data, variogram_object$var_model,
       block = block, ...)
1: autoKrige(zinc ~ 1, meuse)


I would really appreciate any hint about the possible reason of this
error and if it could be overcome in some way.


Thanks in advance for any help.


Mauricio
-- 
============================================
Ph.D. Candidate,
University of Trento
Dept. of Civil and Env. Engineering
Trento / Italy
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