[R] Extracting equation from R code

[tpet]

Dear R-helpers,

I am trying to extract two equations from an R code, but I am not being able
to do it. The code is this:

function (x, fullin, fullout, crossover, infz = 0.953, outfz = 0.047, 
    details = FALSE) 
{
    if (fullin < fullout || crossover < fullout || fullin < crossover) 
        stop("It should be that: fullin > crossover > fullout.")
    var.dev <- x - crossover
    inLogOdd <- log(infz/(1 - infz))
    outLogOdd <- log(outfz/(1 - outfz))
    inScalar <- inLogOdd/(fullin - crossover)
    outScalar <- outLogOdd/(fullout - crossover)
    scalars <- rep(NA, length(x))
    scalars[var.dev > 0] <- inScalar
    scalars[var.dev < 0] <- outScalar
    product <- scalars * var.dev
    fz <- exp(product)/(1 + exp(product))
    if (details) {
        ans <- data.frame(x = x, deviations = var.dev, scalars = scalars, 
            logOdd = product, membership = fz)
    }
    else ans <- fz
    ans
}

I would like to write the equations for fz as a function of x, fullin,
fullout, and crossover.  I believe the code and the math aren’t that
difficult for many of you. Though as you can see, they are for me. The
equations I could arrive at are the following, but I know they are wrong as
their results aren’t the same as the ones derived from the code:

fz = exp(log(0.953/(1 – 0.953))/(fullin - crossover)* (x -
crossover))/(1+exp(log(0.953/(1 – 0.953))/(fullin - crossover)* (x -
crossover)))
for  x > crossover

and

fz = exp(log(0.047/(1 – 0.047))/(fullout - crossover)* (x -
crossover))/(1+exp(log(0.047/(1 – 0.047))/( fullout  - crossover)* (x -
crossover)))
for x < crossover

Does anyone have any ideas about the right equations?

Thank you,

Tiago

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