Expand a Vector into a Symmetric Matrix
This function takes a vector of appropriate length (typically created using
vech) and creates a symmetric matrix.
xpnd(x, nrow = NULL)
x |
A list of elements to expand into symmetric matrix. |
nrow |
The number of rows (and columns) in the returned matrix. Look into the details. |
This function is particularly useful when dealing with variance covariance
matrices. Note that R stores matrices in column major order, and that the
items in x will be recycled to fill the matrix if need be.
The number of rows can be specified or automatically computed from the number of elements in a given object via (-1 + √{(1 + 8 * length(x))}) / 2.
An (nrows \times nrows) symmetric matrix.
xpnd(c(1,2,3,4,4,5,6,7,8,9),4) xpnd(c(1,2,3,4,4,5,6,7,8,9))
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