CODEWITHSUNDEEP
r
jolien
jolien

Reputation: 3

Integration multiple functions

Assume you have the following code

X = cbind(5,3,4)
func <- function(t){
   return(X*t)
}

Then func(5) results in the vector (25,15,20)

Now I want to solve the three integrals int(5t,dt,0,5), int(3t,dt,0,5) and int(4t,dt,0,5). Unfortunately, this does not work with 

integrate(func,lower=0,upper=10)$value

Can someone help me how I can do this without a for loop?

Upvotes: 0

Views: 404

Answers (1)

Bertil Baron
Bertil Baron

Reputation: 5003

OK now I understand.

you can define func to return a function somthing like this

func <- function(t){
    function(v){v*t}
}

now func(5) returns a function that multpies its argument with 5

t <- func(5)
t(5)
[1] 25

now to integrate the three functions you can use lapply

lapply(X,function(t){integrate(func(t),0,5)})

If more variables are needed you can change the code accordingly

func <- function(V,y,w){
    function(t){1/V * pmax.int(-c, pmin.int((y-t)/V,c))*w}
}

only with the list do we need to trix around a bit. I am using the package purrr here to make a list of list each list containg one set of the different variables.

V = c(1,2,3) ;c = 2; y = c(5,6,7); w = c(8,9,10); z = c(8,10,11) 
L <- list(V = V,y = y, w = w,z = z)
L2 <- L %>% transpose()

The final call of the lapply will then look like this.

lapply(L2,function(vars){integrate(func(vars$V,vars$y,vars$w),vars$y,vars$z)})

Upvotes: 2

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