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It seems that many projects slowly come upon a need to do matrix math, and fall into the trap of first building some vector classes and slowly adding in functionality until they get caught building a half-assed custom linear algebra library, and depending on it.
I'd like to avoid that while not building in a dependence on some tangentially related library (e.g. OpenCV, OpenSceneGraph).
What are the commonly used matrix math/linear algebra libraries out there, and why would decide to use one over another? Are there any that would be advised against using for some reason? I am specifically using this in a geometric/time context*(2,3,4 Dim)* but may be using higher dimensional data in the future.
I'm looking for differences with respect to any of: API, speed, memory use, breadth/completeness, narrowness/specificness, extensibility, and/or maturity/stability.
Update
I ended up using Eigen3 which I am extremely happy with.
There are quite a few projects that have settled on the Generic Graphics Toolkit for this. The GMTL in there is nice - it's quite small, very functional, and been used widely enough to be very reliable. OpenSG, VRJuggler, and other projects have all switched to using this instead of their own hand-rolled vertor/matrix math.
I've found it quite nice - it does everything via templates, so it's very flexible, and very fast.
Edit:
After the comments discussion, and edits, I thought I'd throw out some more information about the benefits and downsides to specific implementations, and why you might choose one over the other, given your situation.
GMTL -
Benefits: Simple API, specifically designed for graphics engines. Includes many primitive types geared towards rendering (such as planes, AABB, quatenrions with multiple interpolation, etc) that aren't in any other packages. Very low memory overhead, quite fast, easy to use.
Downsides: API is very focused specifically on rendering and graphics. Doesn't include general purpose (NxM) matrices, matrix decomposition and solving, etc, since these are outside the realm of traditional graphics/geometry applications.
Eigen -
Benefits: Clean API, fairly easy to use. Includes a Geometry module with quaternions and geometric transforms. Low memory overhead. Full, highly performant solving of large NxN matrices and other general purpose mathematical routines.
Downsides: May be a bit larger scope than you are wanting (?). Fewer geometric/rendering specific routines when compared to GMTL (ie: Euler angle definitions, etc).
IMSL -
Benefits: Very complete numeric library. Very, very fast (supposedly the fastest solver). By far the largest, most complete mathematical API. Commercially supported, mature, and stable.
Downsides: Cost - not inexpensive. Very few geometric/rendering specific methods, so you'll need to roll your own on top of their linear algebra classes.
NT2 -
Benefits: Provides syntax that is more familiar if you're used to MATLAB. Provides full decomposition and solving for large matrices, etc.
Downsides: Mathematical, not rendering focused. Probably not as performant as Eigen.
LAPACK -
Benefits: Very stable, proven algorithms. Been around for a long time. Complete matrix solving, etc. Many options for obscure mathematics.
Downsides: Not as highly performant in some cases. Ported from Fortran, with odd API for usage.
Personally, for me, it comes down to a single question - how are you planning to use this. If you're focus is just on rendering and graphics, I like Generic Graphics Toolkit, since it performs well, and supports many useful rendering operations out of the box without having to implement your own. If you need general purpose matrix solving (ie: SVD or LU decomposition of large matrices), I'd go with Eigen, since it handles that, provides some geometric operations, and is very performant with large matrix solutions. You may need to write more of your own graphics/geometric operations (on top of their matrices/vectors), but that's not horrible.
So I'm a pretty critical person, and figure if I'm going to invest in a library, I'd better know what I'm getting myself into. I figure it's better to go heavy on the criticism and light on the flattery when scrutinizing; what's wrong with it has many more implications for the future than what's right. So I'm going to go overboard here a little bit to provide the kind of answer that would have helped me and I hope will help others who may journey down this path. Keep in mind that this is based on what little reviewing/testing I've done with these libs. Oh and I stole some of the positive description from Reed.
I'll mention up top that I went with GMTL despite it's idiosyncrasies because the Eigen2 unsafeness was too big of a downside. But I've recently learned that the next release of Eigen2 will contain defines that will shut off the alignment code, and make it safe. So I may switch over.
Update: I've switched to Eigen3. Despite it's idiosyncrasies, its scope and elegance are too hard to ignore, and the optimizations which make it unsafe can be turned off with a define.
Eigen2/Eigen3
Benefits: LGPL MPL2, Clean, well designed API, fairly easy to use. Seems to be well maintained with a vibrant community. Low memory overhead. High performance. Made for general linear algebra, but good geometric functionality available as well. All header lib, no linking required.
Idiocyncracies/downsides: (Some/all of these can be avoided by some defines that are available in the current development branch Eigen3)
Unsafe performance optimizations result in needing careful following of rules. Failure to follow rules causes crashes.
you simply cannot safely pass-by-value
use of Eigen types as members requires special allocator customization (or you crash)
use with stl container types and possibly other templates required
special allocation customization (or you will crash)
certain compilers need special care to prevent crashes on function calls (GCC windows)
GMTL
Benefits: LGPL, Fairly Simple API, specifically designed for graphics engines.
Includes many primitive types geared towards rendering (such as
planes, AABB, quatenrions with multiple interpolation, etc) that
aren't in any other packages. Very low memory overhead, quite fast,
easy to use. All header based, no linking necessary.
Idiocyncracies/downsides:
API is quirky
what might be myVec.x() in another lib is only available via myVec[0] (Readability problem)
an array or stl::vector of points may cause you to do something like pointsList[0][0] to access the x component of the first point
in a naive attempt at optimization, removed cross(vec,vec) and
replaced with makeCross(vec,vec,vec) when compiler eliminates
unnecessary temps anyway
normal math operations don't return normal types unless you shut
off some optimization features e.g.: vec1 - vec2 does not return a
normal vector so length( vecA - vecB ) fails even though vecC = vecA -
vecB works. You must wrap like: length( Vec( vecA - vecB ) )
operations on vectors are provided by external functions rather than
members. This may require you to use the scope resolution everywhere
since common symbol names may collide
you have to do
length( makeCross( vecA, vecB ) )
or
gmtl::length( gmtl::makeCross( vecA, vecB ) )
where otherwise you might try
vecA.cross( vecB ).length()
not well maintained
still claimed as "beta"
documentation missing basic info like which headers are needed to
use normal functionalty
Vec.h does not contain operations for Vectors, VecOps.h contains
some, others are in Generate.h for example. cross(vec&,vec&,vec&) in
VecOps.h, [make]cross(vec&,vec&) in Generate.h
immature/unstable API; still changing.
For example "cross" has moved from "VecOps.h" to "Generate.h", and
then the name was changed to "makeCross". Documentation examples fail
because still refer to old versions of functions that no-longer exist.
NT2
Can't tell because they seem to be more interested in the fractal image header of their web page than the content. Looks more like an academic project than a serious software project.
Latest release over 2 years ago.
Apparently no documentation in English though supposedly there is something in French somewhere.
Cant find a trace of a community around the project.
LAPACK & BLAS
Benefits: Old and mature.
Downsides:
old as dinosaurs with really crappy APIs
For what it's worth, I've tried both Eigen and Armadillo. Below is a brief evaluation.
Eigen
Advantages:
1. Completely self-contained -- no dependence on external BLAS or LAPACK.
2. Documentation decent.
3. Purportedly fast, although I haven't put it to the test.
Disadvantage:
The QR algorithm returns just a single matrix, with the R matrix embedded in the upper triangle. No idea where the rest of the matrix comes from, and no Q matrix can be accessed.
Armadillo
Advantages:
1. Wide range of decompositions and other functions (including QR).
2. Reasonably fast (uses expression templates), but again, I haven't really pushed it to high dimensions.
Disadvantages:
1. Depends on external BLAS and/or LAPACK for matrix decompositions.
2. Documentation is lacking IMHO (including the specifics wrt LAPACK, other than changing a #define statement).
Would be nice if an open source library were available that is self-contained and straightforward to use. I have run into this same issue for 10 years, and it gets frustrating. At one point, I used GSL for C and wrote C++ wrappers around it, but with modern C++ -- especially using the advantages of expression templates -- we shouldn't have to mess with C in the 21st century. Just my tuppencehapenny.
If you are looking for high performance matrix/linear algebra/optimization on Intel processors, I'd look at Intel's MKL library.
MKL is carefully optimized for fast run-time performance - much of it based on the very mature BLAS/LAPACK fortran standards. And its performance scales with the number of cores available. Hands-free scalability with available cores is the future of computing and I wouldn't use any math library for a new project doesn't support multi-core processors.
Very briefly, it includes:
Basic vector-vector, vector-matrix,
and matrix-matrix operations
Matrix factorization (LU decomp, hermitian,sparse)
Least squares fitting and eigenvalue problems
Sparse linear system solvers
Non-linear least squares solver (trust regions)
Plus signal processing routines such as FFT and convolution
Very fast random number generators (mersenne twist)
Much more.... see: link text
A downside is that the MKL API can be quite complex depending on the routines that you need. You could also take a look at their IPP (Integrated Performance Primitives) library which is geared toward high performance image processing operations, but is nevertheless quite broad.
Paul
CenterSpace Software ,.NET Math libraries, centerspace.net
What about GLM?
It's based on the OpenGL Shading Language (GLSL) specification and released under the MIT license.
Clearly aimed at graphics programmers
I've heard good things about Eigen and NT2, but haven't personally used either. There's also Boost.UBLAS, which I believe is getting a bit long in the tooth. The developers of NT2 are building the next version with the intention of getting it into Boost, so that might count for somthing.
My lin. alg. needs don't exteed beyond the 4x4 matrix case, so I can't comment on advanced functionality; I'm just pointing out some options.
I'm new to this topic, so I can't say a whole lot, but BLAS is pretty much the standard in scientific computing. BLAS is actually an API standard, which has many implementations. I'm honestly not sure which implementations are most popular or why.
If you want to also be able to do common linear algebra operations (solving systems, least squares regression, decomposition, etc.) look into LAPACK.
I'll add vote for Eigen: I ported a lot of code (3D geometry, linear algebra and differential equations) from different libraries to this one - improving both performance and code readability in almost all cases.
One advantage that wasn't mentioned: it's very easy to use SSE with Eigen, which significantly improves performance of 2D-3D operations (where everything can be padded to 128 bits).
Okay, I think I know what you're looking for. It appears that GGT is a pretty good solution, as Reed Copsey suggested.
Personally, we rolled our own little library, because we deal with rational points a lot - lots of rational NURBS and Beziers.
It turns out that most 3D graphics libraries do computations with projective points that have no basis in projective math, because that's what gets you the answer you want. We ended up using Grassmann points, which have a solid theoretical underpinning and decreased the number of point types. Grassmann points are basically the same computations people are using now, with the benefit of a robust theory. Most importantly, it makes things clearer in our minds, so we have fewer bugs. Ron Goldman wrote a paper on Grassmann points in computer graphics called "On the Algebraic and Geometric Foundations of Computer Graphics".
Not directly related to your question, but an interesting read.
FLENS
http://flens.sf.net
It also implements a lot of LAPACK functions.
I found this library quite simple and functional (http://kirillsprograms.com/top_Vectors.php). These are bare bone vectors implemented via C++ templates. No fancy stuff - just what you need to do with vectors (add, subtract multiply, dot, etc).
I'm doing some linear algebra math, and was looking for some really lightweight and simple to use matrix class that could handle different dimensions: 2x2, 2x1, 3x1 and 1x2 basically.
I presume such class could be implemented with templates and using some specialization in some cases, for performance.
Anybody know of any simple implementation available for use? I don't want "bloated" implementations, as I'll running this in an embedded environment where memory is constrained.
Thanks
You could try Blitz++ -- or Boost's uBLAS
I've recently looked at a variety of C++ matrix libraries, and my vote goes to Armadillo.
The library is heavily templated and header-only.
Armadillo also leverages templates to implement a delayed evaluation framework (resolved at compile time) to minimize temporaries in the generated code (resulting in reduced memory usage and increased performance).
However, these advanced features are only a burden to the compiler and not your implementation running in the embedded environment, because most Armadillo code 'evaporates' during compilation due to its design approach based on templates.
And despite all that, one of its main design goals has been ease of use - the API is deliberately similar in style to Matlab syntax (see the comparison table on the site).
Additionally, although Armadillo can work standalone, you might want to consider using it with LAPACK (and BLAS) implementations available to improve performance. A good option would be for instance OpenBLAS (or ATLAS). Check Armadillo's FAQ, it covers some important topics.
A quick search on Google dug up this presentation showing that Armadillo has already been used in embedded systems.
std::valarray is pretty lightweight.
I use Newmat libraries for matrix computations. It's open source and easy to use, although I'm not sure it fits your definition of lightweight (it includes over 50 source files which Visual Studio compiles it into a 1.8MB static library).
CML matrix is pretty good, but may not be lightweight enough for an embedded environment. Check it out anyway: http://cmldev.net/?p=418
Another option, altough may be too late is:
https://launchpad.net/lwmatrix
I for one wasn't able to find simple enough library so I wrote it myself: http://koti.welho.com/aarpikar/lib/
I think it should be able to handle different matrix dimensions (2x2, 3x3, 3x1, etc) by simply setting some rows or columns to zero. It won't be the most fastest approach since internally all operations will be done with 4x4 matrices. Although in theory there might exist that kind of processors that can handle 4x4-operations in one tick. At least I would much rather believe in existence of such processors that than go optimizing those low level matrix calculations. :)
How about just store the matrix in an array, like
2x3 matrix = {2,3,val1,val2,...,val6}
This is really simple, and addition operations are trivial. However, you need to write your own multiplication function.
I would need some basic vector mathematics constructs in an application. Dot product, cross product. Finding the intersection of lines, that kind of stuff.
I can do this by myself (in fact, have already) but isn't there a "standard" to use so bugs and possible optimizations would not be on me?
Boost does not have it. Their mathematics part is about statistical functions, as far as I was able to see.
Addendum:
Boost 1.37 indeed seems to have this. They also gracefully introduce a number of other solutions at the field, and why they still went and did their own. I like that.
Re-check that ol'good friend of C++ programmers called Boost. It has a linear algebra package that may well suits your needs.
I've not tested it, but the C++ eigen library is becoming increasingly more popular these days. According to them, they are on par with the fastest libraries around there and their API looks quite neat to me.
Armadillo
Armadillo employs a delayed evaluation
approach to combine several operations
into one and reduce (or eliminate) the
need for temporaries. Where
applicable, the order of operations is
optimised. Delayed evaluation and
optimisation are achieved through
recursive templates and template
meta-programming.
While chained operations such as
addition, subtraction and
multiplication (matrix and
element-wise) are the primary targets
for speed-up opportunities, other
operations, such as manipulation of
submatrices, can also be optimised.
Care was taken to maintain efficiency
for both "small" and "big" matrices.
I would stay away from using NRC code for anything other than learning the concepts.
I think what you are looking for is Blitz++
Check www.netlib.org, which is maintained by Oak Ridge National Lab and the University of Tennessee. You can search for numerical packages there. There's also Numerical Recipes in C++, which has code that goes with it, but the C++ version of the book is somewhat expensive and I've heard the code described as "terrible." The C and FORTRAN versions are free, and the associated code is quite good.
There is a nice Vector library for 3d graphics in the prophecy SDK:
Check out http://www.twilight3d.com/downloads.html
For linear algebra: try JAMA/TNT . That would cover dot products. (+matrix factoring and other stuff) As far as vector cross products (really valid only for 3D, otherwise I think you get into tensors), I'm not sure.
For an extremely lightweight (single .h file) library, check out CImg. It's geared towards image processing, but has no problem handling vectors.