31 Math libraries and projects

Eigen
7.1 A highlevel C++ library of template headers for linear algebra, matrix and vector operations, numerical solvers and related algorithms. [MPL2] 
TinyExpr
5.7 3.6 L4 Ctiny recursive descent expression parser, compiler, and evaluation engine for math expressions 
linmath.h
5.0 0.0 Ca lean linear math library, aimed at graphics programming. Supports vec3, vec4, mat4x4 and quaternions 
MIRACL
5.0 0.0 L1 CMIRACL Cryptographic SDK: Multiprecision Integer and Rational Arithmetic Cryptographic Library is a C software library that is widely regarded by developers as the gold standard open source SDK for elliptic curve cryptography (ECC). 
NT2
5.0 5.6 C++A SIMDoptimized numerical template library that provides an interface with MATLABlike syntax. [Boost] 
LibTomMath
4.8 2.3 L2 CLibTomMath is a free open source portable number theoretic multipleprecision integer library written entirely in C. 
ExprTK
4.6 0.3 L1 C++C++ Mathematical Expression Parsing And Evaluation Library https://www.partow.net/programming/exprtk/index.html 
Versor
1.8 0.0 ObjectiveC[older version] Versor 1.0 C++ library for conformal geometric algebra draw routines 
Xerus
1.5 0.0 C++A general purpose library for numerical calculations with higher order tensors, TensorTrain Decompositions / Matrix Product States and other Tensor Networks 
Mission : Impossible (AutoDiff)
1.3 0.0 C++A concise C++17 implementation of automatic differentiation (operator overloading) 
SLIMCPP
1.1 7.8 C++Simple Long Integer Math for C++. Lightweight crossplatform headeronly library what implements big integer arithmetic in С++17. 
GMP
A C/C++ library for arbitrary precision arithmetic, operating on signed integers, rational numbers, and floatingpoint numbers. [LGPL3 & GPL2] 
Armadillo
A high quality C++ linear algebra library, aiming towards a good balance between speed and ease of use. The syntax (API) is deliberately similar to Matlab. [MPL2]
* Code Quality Rankings and insights are calculated and provided by Lumnify.
They vary from L1 to L5 with "L5" being the highest.