Index of /code/matrix/

FAQ

What is it?

One day I was bored, so I wrote a matrix class based on the C++ std::vector container. This is the result of my labors.

Can I use it?

Sure, but there's no warranty expressed or implied.

How can I use it?

See the reference.

Should I use it?

Probably not. Here are some other matrix libraries that are actually supported by their authors:

• The Matrix Template Library (MTL) was written by the people behind the Boost Graph Library (BGL).
• Boost.org itself has two components with matrices, uBLAS and boost::multiarray.
• FreePOOMA includes matrix support in the form of the Tensor class.
• Blitz++ claims "performance on par with Fortran 77/90." Its Array class template can be multidimensional.

These libraries are rather heavy-duty, though; I still like my implementation for its (relative) simplicity.

Why is it called eloi::matrix?

I go by the nickname elo[i] on #C++ on EFnet. It's a matrix class. You do the math.

Why did you privately inherit from std::vector?

It's what Herb Sutter calls the "Is Implemented In Terms Of" idiom. Here, a 2D array is implemented in terms of a 1D array:

2D

0	1	2
3	4	5
6	7	8

1D

0

1

2

3

4

5

6

7

8

This is what C++ does under the hood for fixed-size multidimensional arrays (T array[R][C]). This approach also requires less memory than a vector of vectors or a vector of pointers, each of which adds a fixed cost per row. And it's a smidge faster than those, too.

A smidge faster, eh?

Per the results from this program, with minor optimizations enabled, on an Intel Core i7-2720QM running 64-bit Ubuntu Linux:

type	row		column		rand
	init	fetch	init	fetch
T[R*C]	0.30	1.47	11.65	13.82	25.38
T[R][C]	0.27	1.41	11.74	13.82	25.47
T *[R]	0.35	1.39	12.20	14.85	26.75
new T[R*C]	0.29	1.39	12.30	14.26	25.42
new T[R][C]	0.27	1.37	12.24	14.19	26.19
new T *[R]	0.34	1.40	12.85	15.44	27.55
vector<T>	0.28	1.37	12.19	14.14	26.19
vector<vector<T>>	0.35	1.38	13.90	16.25	27.83
vector<T *>	0.33	1.39	12.65	15.34	27.55