R/calcSSB0.R

In nissandjac/PacifichakeMSE: Management strategy evaluation of Pacific hake

### Calculate the Spawning biomass at equilibrium
#' Title
#'
#' @param R0 Unfished recruitment
#' @param Z Total mortality
#' @param nage number of ages
#' @param mat maturity ogive
#'
#' @return
#' @export
#'
#' @examples
#'
calcSSB0 <- function(R0,Z,nage, mat){



age <- 1:nage

M <- rep(Z,nage)

N0 <- NA
N0[1] <- R0
N0[2:(nage-1)] <-R0 * exp(-M[1:(nage-2)]*age[1:(nage-2)])
N0[nage] <- R0*exp(-(M[nage-1]*age[nage-1]))/(1-exp(-M[nage]))# Plus group (ignore recruitment dev's in first year )


SSB.age <- mat*N0*0.5 # In G
SSB_0 <- sum(SSB.age)



return(SSB_0)

}