omxMnor: Multivariate Normal Integration

In OpenMx: Extended Structural Equation Modelling

Multivariate Normal Integration

Description

Given a covariance matrix, a means vector, and vectors of lower and upper bounds, returns the multivariate normal integral across the space between bounds.

Usage

omxMnor(covariance, means, lbound, ubound)

Arguments

covariance	the covariance matrix describing the multivariate normal distribution.
means	a row vector containing means of the variables of the underlying distribution.
lbound	a row vector containing the lower bounds of the integration in each variable.
ubound	a row vector containing the upper bounds of the integration in each variable.

Details

The order of columns in the ‘means’, ‘lbound’, and ‘ubound’ vectors are assumed to be the same as that of the covariance matrix. That is, means[i] is considered to be the mean of the variable whose variance is in covariance[i,i]. That variable will be integrated from lbound[i] to ubound[i] as part of the integration.

The value of ubound[i] or lbound[i] may be set to Inf or -Inf if a boundary at positive or negative infinity is desired.

For all i, ubound[i] must be strictly greater than lbound[i].

The algorithm for multivariate normal integration we use is Alan Genz's FORTRAN implementation of the SADMVN routine described by Genz (1992).

References

Genz, A. (1992). Numerical Computation of Multivariate Normal Probabilities. Journal of Computational Graphical Statistics, 1, 141-149.

Examples

data(myFADataRaw)

covariance <- cov(myFADataRaw[,1:3])
means <- colMeans(myFADataRaw[,1:3])
lbound <- c(-Inf, 0,   1)    # Integrate from -Infinity to 0 on first variable 
ubound <- c(0,    Inf, 2.5)  # From 0 to +Infinity on second, and from 1 to 2.5 on third
omxMnor(covariance, means, lbound, ubound)
# 0.0005995

# An alternative specification of the bounds follows
# Integrate from -Infinity to 0 on first variable 
v1bound = c(-Inf, 0)
# From 0 to +Infinity on second
v2bound = c(0, Inf)
# and from 1 to 2.5 on third
v3bound = c(1, 2.5)
bounds <- cbind(v1bound, v2bound, v3bound)
lbound <- bounds[1,]  
ubound <- bounds[2,]  
omxMnor(covariance, means, lbound, ubound)

OpenMx documentation built on Oct. 19, 2024, 9:06 a.m.