View source: R/ludwig.R View source: R/ludwig.R
ludwig  R Documentation 
Implements the maximum likelihood algorithm for TotalPb/U isochron regression of Ludwig (1998) and extends the underlying methodology to accommodate UThPb data and initial Useries disequilibrium.
ludwig(
x,
model = 1,
anchor = 0,
exterr = FALSE,
type = "joint",
plot = FALSE,
...
)
ludwig(
x,
model = 1,
anchor = 0,
exterr = FALSE,
type = "joint",
plot = FALSE,
...
)
x 
an object of class 
model 
one of three regression models:

anchor 
control parameters to fix the intercept age or common Pb composition of the isochron fit. This can be a scalar or a vector. If If If If 
exterr 
propagate external sources of uncertainty (i.e. decay constants)? 
type 
only relevant if

plot 
logical. Only relevant for datasets with measured
disequilibrium. If 
... 
optional arguments 
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.
a vector with the lower concordia intercept, the common
Pb ratios, the dispersion parameter (if model=3
), and the
initial {}^{234}
U/{}^{238}
U and
{}^{230}
Th/{}^{238}
U activity ratio (in the presence of
initial disequilibrium).
the covariance matrix of par
the degrees of freedom of the model fit (n2
if
x$format<4
or 2n3
if x$format>3
, 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
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
f < system.file("UPb4.csv",package="IsoplotR")
d < read.data(f,method="UPb",format=4)
fit < ludwig(d)
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