Error when integrating "...is not a function, character or symbol"

Question

I have this integration that includes a function. I want to integrate over x values 0-39.

#parameters
alpha <- 0.86
y <- 70000
t <- 600
u <- 5353.65

get_p <- function(x,y,t,u) {
  (((alpha^alpha) * ((1 - alpha)^(1 - alpha)) * (y - t * x)) / u)^(1 / (1 - alpha))
}

integrate(x * get_p(x,y,t,u),lower = 0,upper = 39)

But when I run this code I get the error if I first put x <- 0:

Error in match.fun(f) : 
  'x * get_p(x, y, t, u)' is not a function, character or symbol

And I get this error if I don't specify x first:

Error in match.fun(f) : object 'x' not found

x is not supposed to be defined, we are integrating over i!

What am I doing wrong?

Answer 1

The integrate() function needs a proper function as the first parameter, not an expression. You can use an anonymous function with

integrate(function(x) {x * get_p(x,y,t,u)},lower = 0, upper = 39)

or with the latest lambda syntax

integrate(\(x) {x * get_p(x,y,t,u)},lower = 0, upper = 39)