transMat {AlphaSimR}

Linear transformation matrix

Description

Creates an m by m linear transformation matrix that can be applied to n by m uncorrelated deviates sampled from a standard normal distribution to produce correlated deviates with an arbitrary correlation of R. If R is not positive semi-definite, the function returns smoothing and returns a warning (see details).

Usage

transMat(R)

Arguments

R

a correlation matrix

Details

An eigendecomposition is applied to the correlation matrix and used to test if it is positive semi-definite. If the matrix is not positive semi-definite, it is not a valid correlation matrix. In this case, smoothing is applied to the matrix (as described in the 'cor.smooth' of the 'psych' library) to obtain a valid correlation matrix. The resulting deviates will thus not exactly match the desired correlation, but will hopefully be close if the input matrix wasn't too far removed from a valid correlation matrix.

Examples

# Create an 2x2 correlation matrix
R = 0.5*diag(2) + 0.5

# Sample 1000 uncorrelated deviates from a 
# bivariate standard normal distribution
X = matrix(rnorm(2*1000), ncol=2)

# Compute the transformation matrix
T = transMat(R)

# Apply the transformation to the deviates
Y = X%*%T

# Measure the sample correlation
cor(Y)