src/gromacs/math/matrix.h

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  35 /*! \libinternal
  36  * \file
  37  * \brief Declares special case of 3x3 matrix frequently used, and associated functions.
  38  *
  39  * \author Christian Blau <cblau@gwdg.de>
  40  * \ingroup module_math
  41  */
  42
  43 #ifndef GMX_MATH_MATRIX_H_
  44 #define GMX_MATH_MATRIX_H_
  45
  46 #include <array>
  47
  48 #include "gromacs/math/multidimarray.h"
  49 #include "gromacs/math/utilities.h"
  50 #include "gromacs/math/vec.h"
  51 #include "gromacs/utility/real.h"
  52
  53 namespace gmx
  54 {
  55
  56 /*! \brief Three-by-three matrix of ElementType.
  57  * \tparam ElementType type of element to be stored in matrix
  58  */
  59 template<class ElementType>
  60 using BasicMatrix3x3 = MultiDimArray<std::array<ElementType, 3 * 3>, extents<3, 3>>;
  61
  62 /*! \brief Three-by-three real number matrix.
  63  * \note will replace the C-style real[3][3] "matrix"
  64  */
  65 using Matrix3x3 = BasicMatrix3x3<real>;
  66 //! Convenience alias for a matrix view
  67 using Matrix3x3Span = Matrix3x3::view_type;
  68 //! Convenience alias for a const matrix view
  69 using Matrix3x3ConstSpan = Matrix3x3::const_view_type;
  70
  71 //! Determinant of a 3x3 matrix
  72 constexpr real determinant(Matrix3x3ConstSpan matrix)
  73 {
  74     return (matrix(0, 0) * (matrix(1, 1) * matrix(2, 2) - matrix(2, 1) * matrix(1, 2))
  75             - matrix(1, 0) * (matrix(0, 1) * matrix(2, 2) - matrix(2, 1) * matrix(0, 2))
  76             + matrix(2, 0) * (matrix(0, 1) * matrix(1, 2) - matrix(1, 1) * matrix(0, 2)));
  77 }
  78
  79 //! Calculates the trace of a 3x3 matrix view
  80 constexpr real trace(Matrix3x3ConstSpan matrixView)
  81 {
  82     return matrixView(0, 0) + matrixView(1, 1) + matrixView(2, 2);
  83 }
  84
  85 /*! \brief Create an identity matrix of ElementType with N * M elements.
  86  *
  87  * \tparam ElementType type of matrix elements
  88  * \tparam N number of rows
  89  * \tparam M number of columns, defaults to number of rows if not set
  90  *
  91  * \returns a matrix with values one where row equals column index and null
  92  *          where row does not equal column index
  93  */
  94 template<typename ElementType, int N, int M = N>
  95 MultiDimArray<std::array<ElementType, N * M>, extents<N, M>> identityMatrix()
  96 {
  97     std::array<ElementType, N * M>                               matrixEntries{};
  98     MultiDimArray<std::array<ElementType, N * M>, extents<N, M>> idMatrix(matrixEntries);
  99     for (int i = 0; i < std::min(N, M); i++)
 100     {
 101         idMatrix(i, i) = 1;
 102     }
 103     return idMatrix;
 104 }
 105
 106 //! Calculate the transpose of a 3x3 matrix, from its view
 107 Matrix3x3 transpose(Matrix3x3ConstSpan matrixView);
 108
 109 //! Multiply matrix with vector.
 110 void matrixVectorMultiply(Matrix3x3ConstSpan matrix, RVec* v);
 111
 112 //! Create new matrix type from legacy type.
 113 static inline Matrix3x3 createMatrix3x3FromLegacyMatrix(const matrix legacyMatrix)
 114 {
 115     GMX_RELEASE_ASSERT(legacyMatrix, "Need valid legacy matrix");
 116     Matrix3x3 newMatrix;
 117     for (int i = 0; i < DIM; i++)
 118     {
 119         for (int j = 0; j < DIM; j++)
 120         {
 121             newMatrix(i, j) = legacyMatrix[i][j];
 122         }
 123     }
 124     return newMatrix;
 125 }
 126
 127 //! Fill legacy matrix from new matrix type.
 128 static inline void fillLegacyMatrix(Matrix3x3ConstSpan newMatrix, matrix legacyMatrix)
 129 {
 130     GMX_RELEASE_ASSERT(legacyMatrix, "Need valid legacy matrix");
 131     for (int i = 0; i < DIM; i++)
 132     {
 133         for (int j = 0; j < DIM; j++)
 134         {
 135             legacyMatrix[i][j] = newMatrix(i, j);
 136         }
 137     }
 138 }
 139
 140 } // namespace gmx
 141
 142 #endif