Matrix indicates a matrix. The representative types are `Matrix<complex<float> >` type and `Matrix<float>` type, a matrix of complex numbers and a matrix with real numbers as elements, respectively. `Matrix` type is defined as follows. However, `Base` `Matrix` is the class in which FlowDesigner methods are implemented.

template<class T> class Matrix : public BaseMatrix protected members: int rows; int cols; T *data;

The nodes that use `Matrix` for inter-node communication include MultiFFT (frequency analysis) and LocalizeMUSIC (sound source localization). Further, in a robot audition system with typical functions like sound source location / source tracking / separation and speech recognition for which HARK is used, an ID is given to each sound source in sound source tracking (SourceTracker ). `Matrix` is used for inter-node communication in the processing before an ID is given, and `Map` is often used in processing after that.