[R] Error in JohnsonFit

prajamitra bhuyan prajamitra.bhuyan at gmail.com
Mon Oct 1 05:17:05 CEST 2012

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 #

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)


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.

Prajamitra Bhuyan

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