Eigen defines several typedef shortcuts for most common matrix and vector types.

The general patterns are the following:

MatrixSizeType where Size can be 2,3,4 for fixed size square matrices or X for dynamic size, and where Type can be i for integer, f for float, d for double, cf for complex float, cd for complex double.

For example, Matrix3d is a fixed-size 3x3 matrix type of doubles, and MatrixXf is a dynamic-size matrix of floats.

There are also VectorSizeType and RowVectorSizeType which are self-explanatory. For example, Vector4cf is a fixed-size vector of 4 complex floats.

With [c++11], template alias are also defined for common sizes. They follow the same pattern as above except that the scalar type suffix is replaced by a template parameter, i.e.:

• MatrixSize<Type> where Size can be 2,3,4 for fixed size square matrices or X for dynamic size.
• MatrixXSize<Type> and MatrixSizeX<Type> where Size can be 2,3,4 for hybrid dynamic/fixed matrices.
• VectorSize<Type> and RowVectorSize<Type> for column and row vectors.

With [c++11], you can also use fully generic column and row vector types: Vector<Type,Size> and RowVector<Type,Size>.

See also

class Matrix