问题
I'm having an issue where my specific inputs generate an error.
library(kriging)
x <- c(0.65,0.45,0.25,0.65,0.45,0.25,0.55,0.4,0.25,0.55,0.4,0.25,0.6,0.45,0.25,0.6,0.45,0.25,0.5,0.4,0.25,0.5,0.4,0.25,0.55,0.4,0.25,0.55,0.4,0.25,0.5,0.35,0.25,0.5,0.35,0.25)
y <- c(0.25,0.45,0.65,0.2,0.4,0.6,0.25,0.4,0.55,0.2,0.35,0.5,0.25,0.4,0.6,0.2,0.35,0.55,0.25,0.35,0.5,0.2,0.3,0.45,0.25,0.4,0.55,0.2,0.35,0.5,0.2,0.35,0.45,0.15,0.3,0.4)
r <- c(241.5,236.8333333,229.875,242,235.5,231.3333333,238,236.875,225.75,238.5,233.25,228.5,24,0.5,237.1666667,229.5,241.3333333,236.8333333,227.75,237.625,233.7,228.3333333,236.8,235,229.8333333,238.1,234.6,228.6666667,237.375,235.1,228.6666667,236.4,231.6666667,227.3,236.5,232.625,227.3571429)
x <- data.matrix(x)
x <- sweep(x,1,100,"*")
y <- data.matrix(y)
y <- sweep(y,1,100,"*")
krig <- kriging(x,y,r,lag=3)
Error in solve.default(matrix(A, n + 1, n + 1)) :Lapack routine dgesv: system is exactly singular: U[26,26] = 0
I honestly don't know what's wrong. My formatting seems to be well aligned with example code I've seen.
回答1:
The problem is, as @mrip mentioned, that you have duplicate observations. In this context, points with exactly the same x
and y
coordinates. The following code reveals the duplicates:
coor = cbind(x, y)
duplicated(coor)
# [1] FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE
#[13] FALSE TRUE TRUE FALSE FALSE TRUE FALSE TRUE TRUE FALSE FALSE FALSE
#[25] TRUE TRUE TRUE TRUE TRUE TRUE TRUE FALSE TRUE FALSE FALSE FALSE
coor[duplicated(coor),]
# [,1] [,2]
#[1,] 45 40
#[2,] 25 60
#[3,] 25 55
#[4,] 40 35
#[5,] 25 50
#[6,] 55 25
#[7,] 40 40
#[8,] 25 55
#[9,] 55 20
#[10,] 40 35
#[11,] 25 50
#[12,] 50 20
#[13,] 25 45
This leads to an uninvertible covariance matrix in the kriging equations, which in turn leads to the Lapack error from dgesv
. The solution is to remove the duplicates from the dataset.
The following dataset works:
x = runif(100)
y = runif(100)
z = runif(100)
krig = kriging(x, y, z, lag = 3)
image(krig)
来源:https://stackoverflow.com/questions/29085187/in-r-kriging-gives-system-is-exactly-singular-error