Description Usage Arguments Details Value References See Also Examples
Implements the maximum likelihood algorithm for TotalPb/U isochron regression of Ludwig (1998)
1 2 3 4 5 6 7 8 
x 
an object of class 
... 
optional arguments 
exterr 
propagate external sources of uncertainty (e.g., decay constants)? 
alpha 
cutoff value for confidence intervals 
model 
one of three regression models:

anchor 
control parameters to fix the intercept age or common Pb composition of the discordia fit. This is a twoelement list.

The 3dimensional regression algorithm of Ludwig and Titterington
(1994) was modified by Ludwig (1998) to fit socalled 'Total PbU
isochrons'. These are constrained to a radiogenic endmember
composition that falls on the concordia
line. In its
most sophisticated form, this algorithm does not only allow for
correlated errors between variables, but also between
aliquots. IsoplotR
currently uses this algorithm to
propagate decay constant uncertainties in the total PbU isochron
ages. Future versions of the program will generalise this approach
to other chronometers as well.
a twoelement vector with the lower concordia intercept and initial ^{207}Pb/^{206}Pbratio.
the covariance matrix of par
the degrees of freedom of the model fit (3n3, where n is the number of aliquots).
the mean square of weighted deviates (a.k.a. reduced Chisquare statistic) for the fit.
pvalue of a Chisquare test for the linear fit
the overdispersion, i.e., a threeelement vector with the
estimated standard deviation of the (assumedly) Normal distribution
that underlies the true isochron; and the lower and upper
halfwidths of its 100(1α)\% confidence interval (only
relevant if model = 3
).
Ludwig, K.R., 1998. On the treatment of concordant uraniumlead ages. Geochimica et Cosmochimica Acta, 62(4), pp.665676.
Ludwig, K.R. and Titterington, D.M., 1994. Calculation of ^{230}Th/U isochrons, ages, and errors. Geochimica et Cosmochimica Acta, 58(22), pp.50315042.
concordia
, titterington
,
isochron
1 2 3  f < system.file("UPb4.csv",package="IsoplotR")
d < read.data(f,method="UPb",format=4)
fit < ludwig(d)

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