The ini block controls initial conditions for 'theta' (fixed effects), 'omega' (random effects), and 'sigma' (residual error) elements of the model.
Usage
# S3 method for rxUi
ini(x, ..., envir = parent.frame(), append = NULL)
# S3 method for default
ini(x, ..., envir = parent.frame(), append = NULL)
ini(x, ..., envir = parent.frame(), append = NULL)Arguments
- x
expression
- ...
Other expressions for
ini()function- envir
the
environmentin which unevaluated model expressions is to be evaluated. May also beNULL, a list, a data frame, a pairlist or an integer as specified tosys.call.- append
Reorder theta parameters.
NULLmeans no change to parameter order. A parameter name (as a character string) means to put the new parameter after the named parameter. A number less than or equal to zero means to put the parameter at the beginning of the list. A number greater than the last parameter number means to put the parameter at the end of the list.
Details
The ini() function is used in two different ways. The main way that
it is used is to set the initial conditions and associated attributes
(described below) in a model. The other way that it is used is for updating
the initial conditions in a model, often using the pipe operator.
'theta' and 'sigma' can be set using either <- or = such as
tvCL <- 1 or equivalently tvCL = 1. 'omega' can be set with a
~ such as etaCL ~ 0.1.
Parameters can be named or unnamed (though named parameters are preferred).
A named parameter is set using the name on the left of the assignment while
unnamed parameters are set without an assignment operator. tvCL <- 1
would set a named parameter of tvCL to 1. Unnamed parameters
are set using just the value, such as 1.
For some estimation methods, lower and upper bounds can be set for 'theta'
and 'sigma' values. To set a lower and/or upper bound, use a vector of
values. The vector is c(lower, estimate, upper). The vector may be
given with just the estimate (estimate), the lower bound and
estimate (c(lower, estimate)), or all three (c(lower, estimate,
upper)). To set an estimate and upper bound without a lower bound, set the
lower bound to -Inf, c(-Inf, estimate, upper). When an
estimation method does not support bounds, the bounds will be ignored with a
warning.
'omega' values can be set as a single value or as the values of a
lower-triangular matrix. The values may be set as either a
variance-covariance matrix (the default) or as a correlation matrix for the
off-diagonals with the standard deviations on the diagonals. Names may be
set on the left side of the ~. To set a variance-covariance matrix
with variance values of 2 and 3 and a covariance of -2.5 use ~c(2, 2.5,
3). To set the same matrix with names of iivKa and iivCL, use
iivKa + iivCL~c(2, 2.5, 3). To set a correlation matrix with standard
deviations on the diagonal, use cor() like iivKa + iivCL~cor(2,
-0.5, 3).
Values may be fixed (and therefore not estimated) using either the name
fixed at the end of the assignment or by calling fixed() as a
function for the value to fix. For 'theta' and 'sigma', either the estimate
or the full definition (including lower and upper bounds) may be included in
the fixed setting. For example, the following are all effectively equivalent
to set a 'theta' or 'sigma' to a fixed value (because the lower and upper
bounds are ignored for a fixed value): tvCL <- fixed(1), tvCL <-
fixed(0, 1), tvCL <- fixed(0, 1, 2), tvCL <- c(0, fixed(1),
2), or tvCL <- c(0, 1, fixed). For 'omega' assignment, the full
block or none of the block must be set as fixed. Examples of setting
an 'omega' value as fixed are: iivKa~fixed(1), iivKa +
iivCL~fixed(1, 2, 3), or iivKa + iivCL~c(1, 2, 3, fixed). Anywhere
that fixed is used, FIX, FIXED, or fix may be
used equivalently.
For any value, standard mathematical operators or functions may be used to
define the value. For example, log(2) and 24*30 may be used to
define a value anywhere that a number can be used (e.g. lower bound,
estimate, upper bound, variance, etc.).
Values may be labeled using the label() function after the assignment.
Labels are are used to make reporting easier by giving a human-readable
description of the parameter, but the labels do not have any effect on
estimation. The typical way to set a label so that the parameter tvCL
has a label of "Typical Value of Clearance (L/hr)" is tvCL <- 1;
label("Typical Value of Clearance (L/hr)").
rxode2/nlmixr2 will attempt to determine some
back-transformations for the user. For example, CL <- exp(tvCL) will
detect that tvCL must be back-transformed by exp() for easier
interpretation. When you want to control the back-transformation, you can
specify the back-transformation using backTransform() after the
assignment. For example, to set the
back-transformation to exp(), you can use tvCL <- 1;
backTransform(exp()).
See also
Other Initial conditions:
zeroRe()
Examples
# Set the ini() block in a model
one.compartment <- function() {
ini({
tka <- log(1.57); label("Ka")
tcl <- log(2.72); label("Cl")
tv <- log(31.5); label("V")
eta.ka ~ 0.6
eta.cl ~ 0.3
eta.v ~ 0.1
add.sd <- 0.7
})
model({
ka <- exp(tka + eta.ka)
cl <- exp(tcl + eta.cl)
v <- exp(tv + eta.v)
d/dt(depot) = -ka * depot
d/dt(center) = ka * depot - cl / v * center
cp = center / v
cp ~ add(add.sd)
})
}
# Use piping to update initial conditions
one.compartment %>% ini(tka <- log(2))
#>
#>
#> ℹ change initial estimate of `tka` to `0.693147180559945`
#> ── rxode2-based free-form 2-cmt ODE model ──────────────────────────────────────
#> ── Initalization: ──
#> Fixed Effects ($theta):
#> tka tcl tv add.sd
#> 0.6931472 1.0006319 3.4499875 0.7000000
#>
#> Omega ($omega):
#> eta.ka eta.cl eta.v
#> eta.ka 0.6 0.0 0.0
#> eta.cl 0.0 0.3 0.0
#> eta.v 0.0 0.0 0.1
#>
#> States ($state or $stateDf):
#> Compartment Number Compartment Name
#> 1 1 depot
#> 2 2 center
#> ── μ-referencing ($muRefTable): ──
#> theta eta level
#> 1 tka eta.ka id
#> 2 tcl eta.cl id
#> 3 tv eta.v id
#>
#> ── Model (Normalized Syntax): ──
#> function() {
#> ini({
#> tka <- 0.693147180559945
#> label("Ka")
#> tcl <- 1.00063188030791
#> label("Cl")
#> tv <- 3.44998754583159
#> label("V")
#> add.sd <- c(0, 0.7)
#> eta.ka ~ 0.6
#> eta.cl ~ 0.3
#> eta.v ~ 0.1
#> })
#> model({
#> ka <- exp(tka + eta.ka)
#> cl <- exp(tcl + eta.cl)
#> v <- exp(tv + eta.v)
#> d/dt(depot) = -ka * depot
#> d/dt(center) = ka * depot - cl/v * center
#> cp = center/v
#> cp ~ add(add.sd)
#> })
#> }
one.compartment %>% ini(tka <- label("Absorption rate, Ka (1/hr)"))
#>
#>
#> ── rxode2-based free-form 2-cmt ODE model ──────────────────────────────────────
#> ── Initalization: ──
#> Fixed Effects ($theta):
#> tka tcl tv add.sd
#> 0.4510756 1.0006319 3.4499875 0.7000000
#>
#> Omega ($omega):
#> eta.ka eta.cl eta.v
#> eta.ka 0.6 0.0 0.0
#> eta.cl 0.0 0.3 0.0
#> eta.v 0.0 0.0 0.1
#>
#> States ($state or $stateDf):
#> Compartment Number Compartment Name
#> 1 1 depot
#> 2 2 center
#> ── μ-referencing ($muRefTable): ──
#> theta eta level
#> 1 tka eta.ka id
#> 2 tcl eta.cl id
#> 3 tv eta.v id
#>
#> ── Model (Normalized Syntax): ──
#> function() {
#> ini({
#> tka <- 0.451075619360217
#> label("Absorption rate, Ka (1/hr)")
#> tcl <- 1.00063188030791
#> label("Cl")
#> tv <- 3.44998754583159
#> label("V")
#> add.sd <- c(0, 0.7)
#> eta.ka ~ 0.6
#> eta.cl ~ 0.3
#> eta.v ~ 0.1
#> })
#> model({
#> ka <- exp(tka + eta.ka)
#> cl <- exp(tcl + eta.cl)
#> v <- exp(tv + eta.v)
#> d/dt(depot) = -ka * depot
#> d/dt(center) = ka * depot - cl/v * center
#> cp = center/v
#> cp ~ add(add.sd)
#> })
#> }
# Move the tka parameter to be just below the tv parameter (affects parameter
# summary table, only)
one.compartment %>% ini(tka <- label("Absorption rate, Ka (1/hr)"), append = "tv")
#>
#>
#> ── rxode2-based free-form 2-cmt ODE model ──────────────────────────────────────
#> ── Initalization: ──
#> Fixed Effects ($theta):
#> tcl tv tka add.sd
#> 1.0006319 3.4499875 0.4510756 0.7000000
#>
#> Omega ($omega):
#> eta.ka eta.cl eta.v
#> eta.ka 0.6 0.0 0.0
#> eta.cl 0.0 0.3 0.0
#> eta.v 0.0 0.0 0.1
#>
#> States ($state or $stateDf):
#> Compartment Number Compartment Name
#> 1 1 depot
#> 2 2 center
#> ── μ-referencing ($muRefTable): ──
#> theta eta level
#> 1 tka eta.ka id
#> 2 tcl eta.cl id
#> 3 tv eta.v id
#>
#> ── Model (Normalized Syntax): ──
#> function() {
#> ini({
#> tcl <- 1.00063188030791
#> label("Cl")
#> tv <- 3.44998754583159
#> label("V")
#> tka <- 0.451075619360217
#> label("Absorption rate, Ka (1/hr)")
#> add.sd <- c(0, 0.7)
#> eta.ka ~ 0.6
#> eta.cl ~ 0.3
#> eta.v ~ 0.1
#> })
#> model({
#> ka <- exp(tka + eta.ka)
#> cl <- exp(tcl + eta.cl)
#> v <- exp(tv + eta.v)
#> d/dt(depot) = -ka * depot
#> d/dt(center) = ka * depot - cl/v * center
#> cp = center/v
#> cp ~ add(add.sd)
#> })
#> }
# When programming with rxode2/nlmixr2, it may be easier to pass strings in
# to modify the ini
one.compartment %>% ini("tka <- log(2)")
#>
#>
#> ℹ change initial estimate of `tka` to `0.693147180559945`
#> ── rxode2-based free-form 2-cmt ODE model ──────────────────────────────────────
#> ── Initalization: ──
#> Fixed Effects ($theta):
#> tka tcl tv add.sd
#> 0.6931472 1.0006319 3.4499875 0.7000000
#>
#> Omega ($omega):
#> eta.ka eta.cl eta.v
#> eta.ka 0.6 0.0 0.0
#> eta.cl 0.0 0.3 0.0
#> eta.v 0.0 0.0 0.1
#>
#> States ($state or $stateDf):
#> Compartment Number Compartment Name
#> 1 1 depot
#> 2 2 center
#> ── μ-referencing ($muRefTable): ──
#> theta eta level
#> 1 tka eta.ka id
#> 2 tcl eta.cl id
#> 3 tv eta.v id
#>
#> ── Model (Normalized Syntax): ──
#> function() {
#> ini({
#> tka <- 0.693147180559945
#> label("Ka")
#> tcl <- 1.00063188030791
#> label("Cl")
#> tv <- 3.44998754583159
#> label("V")
#> add.sd <- c(0, 0.7)
#> eta.ka ~ 0.6
#> eta.cl ~ 0.3
#> eta.v ~ 0.1
#> })
#> model({
#> ka <- exp(tka + eta.ka)
#> cl <- exp(tcl + eta.cl)
#> v <- exp(tv + eta.v)
#> d/dt(depot) = -ka * depot
#> d/dt(center) = ka * depot - cl/v * center
#> cp = center/v
#> cp ~ add(add.sd)
#> })
#> }