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Seawas

I would like to plot an integral of a function with a variable upper limit in R. However, the upper limit is not the 'pure' x-coordinate, but a calculation of it. I struggle to pass the calculated x-coordinate to my plot function. Using ggplot2, I have got this far – thanks to Thomas and mnel:

library(ggplot2)

#sample function
f_a   <- function(a) { 2 * a }

#set up integration
int_f <- Vectorize( function( f = f_a , lower = 0, upper , ... ){
            integrate( f , lower , upper , ...)[['value']] } , 'upper' )

#plot it
ggplot( data.frame( b = 0 ) , aes( x = b ) ) + 
    stat_function( fun = int_f , args = list( f = f_a , lower = 0 ) ) +
    xlim( 0 , 4 )

With this, I get a plot of the integrals with b as the upper limits. The thing is, my upper limits are a function of b, say: c(b). My attempts with mappings and other int_f setups have failed as much as my queries here on stackoverflow.

Would be amazing if someone brilliant of this community could show me how to get this thing solved.

Nebukor
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1 Answers1

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Found out myself. Embarrassingly cheap solution (with c() as the function for the upper limit):

...

int_f <- Vectorize( function( f = f_a , lower = 0, upper , ... ){
            integrate( f , lower , c(upper) , ...)[['value']] } , 'upper' )
...

Hope it helps someone!

Nebukor
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