fixstart function

Attempt to Fix Starting Values

This function attempts to fix starting values by comparing the analytic gradient to a numerically approximated gradient. Parameters with a difference between the analytic and numeric gradient that exceeds 'maxdiff' will be reduced by a factor of 'reduce' in each iteration until the average absolute difference between analytic and numeric gradients is lower than 'tol'. Only off-diagonal elements in omega, sigma, kappa, lowertri or rho matrices or any element in beta matrices are adjusted.

fixstart(x, reduce = 0.5, maxdiff = 0.1, tol = 0.01, maxtry = 25)

Arguments

• x: A 'psychonetrics' model
• reduce: The factor with which problematic parameters are reduced in each iteration.
• maxdiff: Maximum difference between analytic and numeric gradient to be considered problematic.
• tol: Average absolute difference between analytic and numeric gradient that is considered acceptable.
• maxtry: Maximum number of iterations to attempt to fix starting values.

Author(s)

Sacha Epskamp