## Revision of mxMatrix Help from Fri, 11/20/2009 - 07:02

The revisions let you track differences between multiple versions of a post.

Wiki home page

Please add material here as you learn...

If you have questions not answers, then add those here: That's how a wiki works.

#### Basic Examples

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

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

#### Get the row or column count of an mxMatrix

```	myMatrix <- mxMatrix('Full', 3, 5)
nrow(myMatrix)
ncol(myMatrix)```

#### Square bracket substitution to set labels

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"
)```

Is the same as setting the labels of matrix B to this:
```	bLabels = c(
"A[1,1]", "b2",
"b3",     "b4"
)```

Both methods forces cell B[1,1] to take the same value as A[1,1].

the benfit of the [] syntax is 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.