when we create a function why we use -(minus) in return in R -

when create function why use -(minus) in return, in r program see example

f <- function(pars) {   l <- (n*log(pars[1]))+(n*pars[1]*log(t1))+(n*pars[1]*log(pars[2]))-        (n*log((t1^pars[1])-(pars[2]^pars[1])))- ((pars[1]+1)*sum(log(pars[2]+x)))   return(-l)   } 

here why use (-l) in return if use return (l)

the sourse of example error in f(x, ...) : argument "x" missing, no default in nlm

usually aim of maximization. when optimizing functions in r default set of optimizing functions minimize. short cut use - sign in log likelihood function on being minimized in turn maximized. although not necessary. can able use controls within optimizing functions indicate whether need maximize or minimize log likelihood function