differential equations - What does [,i] do in R?

Question

I am new to coding and I am currently looking at an R code that I found online. The full code can be found at this link: http://epirecip.es/epicookbook/chapters/kr08/3_4/r_desolve

I am trying to understand the language a bit better, so I had a few questions about this portion of the code here:

# differential equations
diff_eqs <- function(times, Y, parms){
  dY <- numeric(length(Y))
  with(parms,{
    # creates an empty matrix               
    for(i in 1:m){
      dY[i] <- nu[i]*n[4] -  beta[,i]%*%Y[2*m + seq(1:m)] * Y[i] - mu[i] * Y[i] # S_i
      dY[m+i] <-  beta[,i] %*% Y[2*m + seq(1:m)] *Y[i] - mu[i] * Y[m+i] - sigma * Y[m+i] #E_i
      dY[2*m+i] <- sigma * Y[m+i] - gamma * Y[2*m + i] - mu[i] * Y[2*m+i] #I_i
      dY[3*m+i] <- gamma * Y[2*m+i] - mu[i] * Y[3*m + i] #R_i
    }
    list(dY) 
  })
}

In R, what does [,i] mean? And what is the difference between say [,i] and [i] in the context of this system of of equations?

question from:https://stackoverflow.com/questions/65849389/what-does-i-do-in-r

Answer 1

Waitting for answers