R/gdm_numdiff_index.R

In alexanderrobitzsch/CDM: Cognitive Diagnosis Modeling

## File Name: gdm_numdiff_index.R
## File Version: 0.09

####################################################################
# general function for numerical differentiation
# diffindex aggregates across super items
gdm_numdiff_index <- function( pjk, pjk1, pjk2, n.ik,
        max.increment, numdiff.parm, eps=1E-10 )
{
    h <- numdiff.parm
    an.ik <- aperm( n.ik, c(2,3,1) )
    #--- log-likelihood
    ll0 <- cdm_calc_ll_with_counts( an.ik=an.ik, pjk=pjk )
    ll1 <- cdm_calc_ll_with_counts( an.ik=an.ik, pjk=pjk1 )
    ll2 <- cdm_calc_ll_with_counts( an.ik=an.ik, pjk=pjk2 )

    #--- derivatives
    res <- cdm_ll_numerical_differentiation( ll0=ll0, ll1=ll1, ll2=ll2, h=h )
    d1 <- res$d1
    d2 <- res$d2
    #--- calculate increment
    res <- cdm_calc_increment( d1=d1, d2=d2, max.increment=max.increment, type=2 )
    increment <- res$increment
    #--- output
    res <- list(increment=increment, d1=d1, d2=d2, ll0=ll0)
    return(res)
}


.gdm.numdiff.index <- gdm_numdiff_index