logspace.add {DPQ}  R Documentation 
Logspace Arithmetix – Addition and Subtraction
Description
Compute the log(arithm) of a sum (or difference) from the log of terms without causing overflows and without throwing away large handfuls of accuracy.
logspace.add(lx, ly)
:=
\log (\exp (lx) + \exp (ly))
logspace.sub(lx, ly)
:=
\log (\exp (lx)  \exp (ly))
Usage
logspace.add(lx, ly)
logspace.sub(lx, ly)
Arguments
lx , ly 
numeric vectors, typically of the same

Value
a numeric
vector of the same length as x+y
.
Note
This is really from R's C source code for pgamma()
, i.e.,
‘<R>/src/nmath/pgamma.c’
The function definitions are very simple, logspace.sub()
using log1mexp()
.
Author(s)
Morten Welinder (for R's pgamma()
); Martin Maechler
See Also
Examples
set.seed(12)
ly < rnorm(100, sd= 50)
lx < ly + abs(rnorm(100, sd=100)) # lx  ly must be positive for *.sub()
stopifnot(exprs = {
all.equal(logspace.add(lx,ly),
log(exp(lx) + exp(ly)), tol=1e14)
all.equal(logspace.sub(lx,ly),
log(exp(lx)  exp(ly)), tol=1e14)
})
[Package DPQ version 0.58 Index]