Using the C++ Math Library

Selecting a Matrix

Use a matrix index to select a matrix. A matrix index works just like a vector index, except the result is a matrix rather than a vector. For example, let B be the index matrix:

1 2
3 2

Then, A(B) is:

1 2
3 2

Note that the example matrix A was chosen so that A(X) = X for all types of one-dimensional indexing. This is not generally the case. For example, if A were changed to A = magic(3),

8 1 6
3 5 7
4 9 2

then A(B) would equal

8 3
4 3

Note    In both cases, size(A(B)) is equal to size(B). This is a fundamental property of one-dimensional indexing.

Selecting a Vector

Selecting the Entire Matrix As a Column Vector