I’m trying to obtain the three parameters of the Weibull function, using the Maximum likelihood method for diameter. But I need the parameters by group.

For example: I have columns of diameter, plots 1,2, and 3, Ages 2,4,5 and,6, and densities of 200 and 300.

I need parameters for each plot, for all three ages, for the two densities.

Does anyone know how I can do that?

data_DBH <-c(9.2, 10.7, 11.5, 10.2, 10.8, 9.4, 10.4, 9.8, 7.5, 9.6, 9.8, 11.5, 9.7, 8.8, 9.3, 8.8, 9.3, 10.2, 9.7, 9.6, 8.4, 8.4, 8.1, 10.2, 9.8, 9.5, 10.6, 9.5, 9.3, 10.8, 10.4, 9, 9.3)

dweibull3 <- function(x, gamma, beta, alpha) {
(gamma/beta)*((x - alpha)/beta)^(gamma - 1) *
(exp(-((x - alpha)/beta)^gamma)) }

ll.w3 <- function(p, data)
sum(log(dweibull3(data, p[1], p[2], p[3])))

mle.w3.nm <- optim(c(gamma =  9, beta = 8, alpha = 0),
                ll.w3,
                data =data_DBH,
                hessian = TRUE,
                control = list(fnscale = -1))
mle.w3.nm$par