# Revision of mxmatrix-help from Thu, 09/24/2009 - 18:40

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TODO: basic information on using mxMatrix() to go here

## Square bracket substitution

This feature allows you to construct MxMatrix objects, the labels of which refer to another MxMatrix or MxAlgebra. This is done by specifying the name, row, and col of the target matrix or algebra as you would expect to be able to in R, i.e., "foo[row,col]".

The effect of pointing to another cell using bracket notation is just the same as setting the label of the two cells to the same value.

So, given a matrix A with labels:

    aLabels = c(
"a1", "a2",
"a3", "a4",
)


Setting the labels of matrix B to this:

    bLabels = c(
"a1", "b2",
"b3", "b4",
)
#forces cell B[1,1] to take the same value as A[1,1]


Is the same as setting the labels of matrix B to this:

    bLabels = c(
"A[1,1]", "b2",
"b3",     "b4",
)
#forces cell B[1,1] to take the same value as A[1,1]


Benefits of this system are that you only need to set one label to equate two cells, and you don't need to know what label the other cell has currently, just its location.

Caveates: This feature of substitution applies only to matrix labels and cannot be used in mxAlgebra expressions.

### Examples

    require(OpenMx)
A <- mxMatrix('Full', 1, 1, values = 1, name = 'A')
B <- mxMatrix('Full', 1, 1, values = 2, name = 'B')
C <- mxMatrix('Full', 1, 1, values = 3, name = 'C')
D <- mxMatrix('Full', 3, 1, labels = c('A[1,1]', 'B[1,1]', 'C[1,1]'), name = 'D')
model <- mxModel('model', A, B, C, D)
fit <- mxRun(model)
mxEval(D, fit)

    A <- mxMatrix('Full', 2, 2, values = c(1,2,3,4), byrow = TRUE, name = 'A')
B <- mxAlgebra(A + A, name = 'B')
C <- mxMatrix('Full', 2, 2, labels = c('B[2,2]', 'B[2,1]',
'B[1,2]', 'B[1,1]'), byrow = TRUE, name = 'C')
model <- mxModel('model', A, B, C)
fit <- mxRun(model)
mxEval(C, fit)