这是一种方法。
f.X <- function(x) dnorm(x,1,0.5) # normal (mu=1.5, sigma=0.5)
f.Y <- function(y) dlnorm(y,1.5, 0.75) # log-normal (mu=1.5, sigma=0.75)
# convolution integral
f.Z <- function(z) integrate(function(x,z) f.Y(z-x)*f.X(x),-Inf,Inf,z)$value
f.Z <- Vectorize(f.Z) # need to vectorize the resulting fn.
set.seed(1) # for reproducible example
X <- rnorm(1000,1,0.5)
Y <- rlnorm(1000,1.5,0.75)
Z <- X + Y
# compare the methods
hist(Z,freq=F,breaks=50, xlim=c(0,30))
z <- seq(0,50,0.01)
lines(z,f.Z(z),lty=2,col="red")
使用包同样的事情distr
.
library(distr)
N <- Norm(mean=1, sd=0.5) # N is signature for normal dist
L <- Lnorm(meanlog=1.5,sdlog=0.75) # same for log-normal
conv <- convpow(L+N,1) # object of class AbscontDistribution
f.Z <- d(conv) # distribution function
hist(Z,freq=F,breaks=50, xlim=c(0,30))
z <- seq(0,50,0.01)
lines(z,f.Z(z),lty=2,col="red")