library（gam）

data <- read.csv("C:\\Users\\user\\Desktop\\1.csv", header=TRUE)

f <- 0;ok <- TRUE

while (ok) {

for (i in 1:3) {

ep <- y - rowSums(f[, -i])

b <- smooth.spline(x[, i], ep, df = edf)

f[, i] <- predict(b, x[, i])$y

}

rss <- sum((y - rowSums(f))^2)

if (abs(rss - rss0) < 1e-6*rss) ok <- FALSE;

rss0 <- rss