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library(foreach)
# Define a function that creates an iterator that returns subvectors
ivector <- function(x, chunks) {
n <- length(x)
i <- 1
nextEl <- function() {
if (chunks <= 0 || n <= 0) stop('StopIteration')
m <- ceiling(n / chunks)
r <- seq(i, length=m)
i <<- i + m
n <<- n - m
chunks <<- chunks - 1
x[r]
}
obj <- list(nextElem=nextEl)
class(obj) <- c('abstractiter', 'iter')
obj
}
# Define the coordinate grid and figure out how to split up the work
x <- seq(-10, 10, by=0.1)
cat('Running sequentially\n')
ntasks <- 4
# Compute the value of the sinc function at each point in the grid
z <- foreach(y=ivector(x, ntasks), .combine=cbind) %do% {
y <- rep(y, each=length(x))
r <- sqrt(x ^ 2 + y ^ 2)
matrix(10 * sin(r) / r, length(x))
}
# Plot the results as a perspective plot
persp(x, x, z, ylab='y', theta=30, phi=30, expand=0.5, col="lightblue")
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