Matvec Users’ Guide

3.3. MANIPULATION 17
3.2.2 Relational operators
There are six relational operators, they operate between two objects.
== equal to
!= not equal to
< less than
> greater than
= greater than or equal to
These six operators are based on element-by-element comparison. It returns a matrix with resulting
element(i,j) = 1.0 if the relationship is true, otherwise resulting element(i,j) = 0.0
3.2.3 Logical operators
There are two sets of logical operators: (&&, ||) and (.&&, .||).
The && is a short-circuit logical operator AND. A && B returns 1 if both A and B are true (B is evaluated
only after A is true), otherwise return 0. If A (or B) is a matrix, then A.all().all() is implicitly applied. If
A (or B) is a vector, then A.all() is implicitly applied. Any other types of objects will be determined false.
The || is a short-circuit logical operator OR. A || B returns 1 if either A and B are true (B is evaluated
only after A is false), otherwise return 0. If A (or B) is a matrix, then A.all().all() is implicitly applied. If
A (or B) is a vector, then A.all() is implicitly applied. Any other types of objects will be determined false.
The .&& and .|| are the same as && and || except that 1) the former is performed element-by-element,
2) the former is non-short-circuit, thus both operands will be evaluated.
For readability, Matvec creates synonyms AND and OR for && and ||, respectively.
3.3 Manipulation
Matrix manipulation is a tricky work. Basically, there are three kinds of manipulations: 1) accessing elements
and sub-matrices, 2) adjoining and stacking, 3) selecting elements which satisfy whatever condition you
specify. They are described below in detail.
3.3.1 Accessing element and sub-matrix
• accessing an element
A(i,j) accesses (i,j)’th element with boundary checking
• accessing a row
A(i,*) gets a copy of the i’th row of matrix A.
• accessing a column
A(*,j) gets a copy of the j’th column of matrix A.
• accessing sub-matrix
A(i1:i2, j1:j2) returns a sub-matrix of A with row i1 through i2 and column j1 through j2. A([i1,i2,i3],
[j1,j2,j3]) returns a sub-matrix of A with rows i1, i2, and i3 and columns j1, j2, and j3.
For example,