Message-ID: <CAF6S6J-rQN4buGy1SoE0AjB=H0srHd_BRtbEKPYQzCM3Nx5c7g@mail.gmail.com>
Date: 2012-10-01T03:17:05Z
From: prajamitra bhuyan
Subject: Error in JohnsonFit
Dear Sir/Madam,
As mentioned in help, R reports error while fitting Johnson distribution by
method of moments. I have used moments from Weibull distribution and
hence it is well within the feasible
area and try to fit Johnson distribution using method of moments.
As for example,
shape=0.5 # Shape Parameter of IID Weibull Stress #
scale=1 # Scale Parameter of IID Weibull Stress #
# kth order raw moment of Weibull #
k_raw= function(k) (scale^k)*(gamma(1+k/shape))
# Cumulants #
k1=k_raw(1)
k2=k_raw(2)-(k_raw(1))^2
k3=k_raw(3)-3*k_raw(2)*k_raw(1)+3*(k_raw(1))^3 -(k_raw(1))^3
k4=k_raw(4)-4*k3*k1-3*(k2)^2 - 6*(k2)*(k1)^2-(k1)^4
# Central Moments #
theta=c( k1, k2 , k3 , k4+3*(k2)^2)
parms<-JohnsonFit(theta,moment="use")
Error in JohnsonFit(theta, moment = "use") :
Couldn't do an Sb fit
I will be thankful if you please let me know elaborately the exact
difficulty which causes such errors.
Regards,
Prajamitra Bhuyan