Using the C Math Library

Using a Logical Matrix as a One-Dimensional Index

When you use a logical matrix as an index, the result is a column vector. For example, if the logical index matrix B equals

1 0 1
0 1 0
1 0 1

Then

mlfAssign(&X, mlfIndexRef(A, "(?)", B));

equals

1
3
5
7
9

Notice that B has ones at the corners and in the center, and that the result is a column vector of the corner and center elements of A.

Note that you can create B by calling mlfAssign(&B, mlfLogical(matrix)) where matrix stores a matrix of 1's and 0's.

If the logical index is not the same size as the subscripted array, the logical index is treated like a vector. For example, if B = logical([1 0; 0 1]), then

mlfAssign(&X, mlfIndexRef(A, "(?)", B));

equals

1
4

since B has a zero at positions 2 and 3 and a 1 at positions 1 and 4. Logical indices behave just like regular indices in this regard.

Overview

Using Two Logical Vectors as Indices