Hello,
The following code might not be the best way of computing the integrals
for all combinations of the arguments but it gets the job done and I
believe it's readable code.
f2 <- function(a, b, c){
integrate(function(x) {exp(-a*x^3 - b*x^2 - c*x)},
lower = 0, upper = Inf)
}
f2_all_args <- function(a, b, c){
lapply(a, function(.a)
lapply(b, function(.b)
lapply(c, function(.c)
f2(.a, .b, .c)[1:2]
)
)
)
}
a <- seq(from = 0, to = 1, by = 0.5)
b <- seq(from = 5, to = 10, by = 1)
m <- seq(from = 10, to = 20, by = 5)
res <- f2_all_args(a, b, m)
r <- array(0, c(3, 6, 3))
r.error <- array(0, c(3, 6, 3))
for(i in seq_along(a)){
res_i <- res[[i]]
for(j in seq_along(b)){
res_i_j <- res_i[[j]]
for(k in seq_along(m)){
r[i, j, k] <- res_i_j[[k]]$value
r.error[i, j, k] <- res_i_j[[k]]$abs.error
}
}
}
Hope this helps,
Rui Barradas
Às 21:14 de 10/08/19, ravi via R-help escreveu:
Bert,Thanks a lot for your help. I have a few follow-up questions (shown in
the comment lines). Numerical values and error for a (i) vector and (ii) array.
a <- seq(from=0,to=1,by=0.5)
b <- seq(from=5,to=10,by=1)
m <- seq(from=10,to=20,by=5)
f2 <- function(a,b,m)integrate(function(x){exp(-a*x^3-b*x^2-m*x)},lower=0,upper
= Inf)
fv <- Vectorize(f2,vectorize.args=c("a","b","m"),SIMPLIFY=TRUE)
r1 <- fv(a,b,m)
# How to get just the numerical results as an array
# for scalar values of a,b and m, I can get it with
#s <- integrate(f,0,Inf)$value
# How do I get this for a vector
# Finally, if I want an array for all the values of a, b and m, how should I
proceed?
r <- array(0,c(3,6,3))
r.error <- array(0,c(3,6,3))
# I want the results of the vectorized integrate function in the above arrays.
How do I extract these values?
Thanks,Ravi
On Saturday, 10 August 2019, 20:03:22 CEST, Bert Gunter
<[email protected]> wrote:
Ravi:
First of all, you're calling Vectorize incorrectly. The first argument must be
a function *name*, not a function call. Here's what you need to do (and thanks
for the reprex -- wouldn't have been able to help without it!):
f2 <- function(a,b,c)integrate(function(x){exp(-a*x^3-b*x^2-c*x)},lower
=0,upper = Inf)
fv <- Vectorize(f2,vectorize.args=c("a","b","c"),SIMPLIFY=TRUE)
Second of all, as you may realize, the vectorization uses mapply() and so vectorizes the c(a,b,c)
triplet "in parallel," which will "recycle" shorter arguments to the length of
longer. Hence you will get 6 results from your example:
fv(a,b,m)
[,1] [,2] [,3] [,4] [,5]
[,6]
value 0.09207851 0.0635289 0.04837997 0.08856628 0.06224138
0.04777941
abs.error 3.365173e-08 3.108388e-06 1.00652e-09 3.284876e-09 1.796619e-08
6.348142e-09
subdivisions 2 1 2 2 2 2
message "OK" "OK" "OK" "OK" "OK"
"OK"
call Expression Expression Expression Expression Expression
Expression
Cheers,Bert
Bert Gunter
"The trouble with having an open mind is that people keep coming along and sticking
things into it."
-- Opus (aka Berkeley Breathed in his "Bloom County" comic strip )
On Sat, Aug 10, 2019 at 10:20 AM ravi via R-help <[email protected]> wrote:
Hi all,I am having some difficulties in vectorizing the integrate function. Let
me explain with an example.
a <- 10; b <- 3; c <- 4
f <- function(x) {exp(-a*x^3-b*x^2-c*x)}
integrate(f,0,Inf) # works fine
My difficulties start when I want to vectorize.
# attempts to vectorize fail
a <- seq(from=0,to=1,by=0.5)
b <- seq(from=5,to=10,by=1)
m <- seq(from=10,to=20,by=5)
f2 <- function(x,a,b,c) {exp(-a*x^3-b*x^2-m*x)}
fv <- Vectorize(integrate(f2,0,Inf),vectorize.args=c("a","b","m"),SIMPLIFY=TRUE)
I want the result as a 3-d array with dimensions of the lengths of a, b and c.
I have tried several variants but am not having much luck. Will appreciate any
help that I can get.
Thanks,Ravi Sutradhara
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[email protected] mailing list -- To UNSUBSCRIBE and more, see
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
______________________________________________
[email protected] mailing list -- To UNSUBSCRIBE and more, see
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
