B. Jonathan B. Jonathan wrote:
>
> Hi there, I have following equations to be solved for a and b:
>
> a/(a+b) = x1
> ab/((a+b)^2 (a+b+1)) = x2
>
> Is there any direct function available to solve them without
> disentangling them manually? Thanks for your help.
>
There is a package nleqslv that will solve a system of equations with either
a Newton or Broyden method.
You can do this
library(nleqslv)
# trial values
x1 <- .6
x2 <- .2
eqn <- function(par) {
a <- par[1]
b <- par[2]
f <- numeric(2)
f[1] <- a/(a+b) - x1
f[2] <- a*b/((a+b)^2 * (a+b+1)) - x2
f
}
pstart <- c(1,1)
nleqslv(pstart,eqn,control=list(trace=1))
#or this if you don't need the trace
nleqslv(pstart,eqn)
There is also a package BB that uses different methods and is especially
geared towards very large systems.
Berend
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