SafetyMargin: Evaluation of safety margin form the given (Kr,Lr) point
In ShinsukeSakai0321/FFS:

After drawing a line from origin to the evaluation point and extrapolating to the R6 flaw curve, the cross point is calculated using Newton-Raphson method. From the cross point and the evaluation point,

1	SafetyMargin(Kr = 0.3, Lr = 0.5)

`Kr`
`Lr`

##---- Should be DIRECTLY executable !! ----
##-- ==>  Define data, use random,
##--	or do  help(data=index)  for the standard data sets.

## The function is currently defined as
function (Kr = 0.3, Lr = 0.5)
{
    f <- function(x) {
        R6Option1(x) - Kr * x/Lr
    }
    aa <- uniroot(f, c(0, 1.6))
    aa$root/Lr
  }