Using the C++ Math Library

The mwIndex Class

mwArray overloads the () operator for MATLAB-like indexing. The mwArray::operator() functions can accept mwIndex objects. An mwIndex can represent a single integer, a sequence of integers specified by a tuple (start, step, stop), or an arbitrary vector of integers. Array subscripts are always integers; the MATLAB C++ Math Library truncates floating-point numbers to integers in indexing expressions.

You can create mwIndex objects in several ways. The way most familiar to MATLAB users is the colon() function. An mwIndex constructor exists for each form of the colon() function, as this table demonstrates.

Note    The default mwIndex constructor (entry one in the table below) produces an mwIndex object representing : (colon).

Table 4-2: mwIndex Class and the colon() Function 

Description	MATLAB Expression	C++ colon() Equivalent	mwIndex Constructor
All elements of X	X(:)	X(colon())	mwIndex k; X(k)
First 10 elements of row 1	X(1,1:10)	X(1,colon(1,10))	mwIndex k(1,10); X(k)
Elements 2,4,6,8,10 of X	X(2:2:10)	X(colon(2,2,10))	mwIndex k(2,2,10); X(k)

C++ and MATLAB Indexing Syntax

Programming Efficient Indices