R/nr.numdiff.R

In alexanderrobitzsch/sirt: Supplementary Item Response Theory Models

## File Name: nr.numdiff.R
## File Version: 0.09


nr.numdiff <- function( ll0, ll1, ll2, h, eps=10^(-10) )
{
    d1 <- ( ll1 - ll2  ) / ( 2 * h )    # negative sign?
    # second order derivative
    # f(x+h)+f(x-h)=2*f(x) + f''(x)*h^2
    d2 <- ( ll1 + ll2 - 2*ll0 ) / h^2
    d2 <- ifelse( abs(d2) < eps, eps, d2 )
    delta.change <- - d1 / d2
    return(delta.change)
}