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The following message appears while running DiceKriging (in R) with full 2nd order polynamial (2D):

Error in model.frame.default(object, data, xlev = xlev) :
Variablenlängen sind unterschiedlich (gefunden für 'I(inputs[, 1]^2)')

In English:

Variable lengths differ (found for 'I (inputs [1] ^ 2)')

Script:

#Modeling

    xa<-c(1,2,3,4,5,6)
    xb<-c(1,2,3,4,5,6)
    inputs<-expand.grid(xa,xb)
    output<-c(1,4,7,18,23,35,1,4,9,18,23,35,1,4,7,18,1,35,1,4,7,18,35,35,1,4,7,18,23,35,1,4,7,18,23,35)
    m2 <- km(formula = ~.^2 + I(inputs[,1]^2) + I(inputs[,2]^2), design = data.frame(x = inputs), response = output)

#prediction

    x11 <- seq(1,6, by = 0.1)
    x22 <- seq(1,6, by = 0.1)
    DESIGNX <- expand.grid(x11, x22)
    newdata <- data.frame(x = DESIGNX)
    DESIGNY <- predict(m2, newdata, "UK")$mean

#Error in model.frame.default(object, data, xlev = xlev) : 
 # variable lengths differ (found for 'I(inputs[, 1]^2)')
Prune
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NMF
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1 Answers1

1

When you use, design = data.frame(x = inputs), this create a data.frame with column names x.Var1 and x.Var2. Using these names in the formula solves the problem:

m2 <- km(formula = ~.^2 + I(x.Var1^2) + I(x.Var2^2), design = data.frame(x = inputs), response = output)

It may be better to define your own names, and reusing the same names in newdata:

design <- data.frame(inputs); names(design) <- c("x1", "x2")
m2 <- km(formula = ~.^2 + I(x1^2) + I(x2^2), design = design, response = output)

newdata <- data.frame(DESIGNX); names(newdata) <- names(design)
DESIGNY <- predict(m2, newdata, "UK")$mean
Olivier
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