MatrixVectorMult
org.ejml.alg.dense.mult

Class MatrixVectorMult



  • public class MatrixVectorMultextends Object

    This class contains various types of matrix vector multiplcation operations for DenseMatrix64F.

    If a matrix has only one column or row then it is a vector. There are faster algorithms that can be used to multiply matrices by vectors. Strangely, even though the operations count smaller, the difference between this and a regular matrix multiply is insignificant for large matrices. The smaller matrices there is about a 40% speed improvement. In practice the speed improvement for smaller matrices is not noticeable unless 10s of millions of matrix multiplications are being performed.

    • Constructor Detail

      • MatrixVectorMult

        public MatrixVectorMult()
    • Method Detail

      • mult

        public static void mult(RowD1Matrix64F a,        D1Matrix64F b,        D1Matrix64F c)

        Performs a matrix vector multiply.

        c = A * b
        and
        c = A * bT

        ci = Sum{ j=1:n, aij * bj}

        where A is a matrix, b is a column or transposed row vector, and c is a column vector.

        Parameters:
        a - A matrix that is m by n. Not modified.
        b - A vector that has length n. Not modified.
        c - A column vector that has length m. Modified.
      • multAdd

        public static void multAdd(RowD1Matrix64F A,           D1Matrix64F B,           D1Matrix64F C)

        Performs a matrix vector multiply.

        C = C + A * B
        or
        C = C + A * BT

        ci = Sum{ j=1:n, ci + aij * bj}

        where A is a matrix, B is a column or transposed row vector, and C is a column vector.

        Parameters:
        A - A matrix that is m by n. Not modified.
        B - A vector that has length n. Not modified.
        C - A column vector that has length m. Modified.
      • multTransA_small

        public static void multTransA_small(RowD1Matrix64F A,                    D1Matrix64F B,                    D1Matrix64F C)

        Performs a matrix vector multiply.

        C = AT * B
        where B is a column vector.
        or
        C = AT * BT
        where B is a row vector.

        ci = Sum{ j=1:n, aji * bj}

        where A is a matrix, B is a column or transposed row vector, and C is a column vector.

        This implementation is optimal for small matrices. There is a huge performance hit when used on large matrices due to CPU cache issues.

        Parameters:
        A - A matrix that is m by n. Not modified.
        B - A that has length m and is a column. Not modified.
        C - A column vector that has length n. Modified.
      • multAddTransA_small

        public static void multAddTransA_small(RowD1Matrix64F A,                       D1Matrix64F B,                       D1Matrix64F C)

        Performs a matrix vector multiply.

        C = C + AT * B
        or
        C = CT + AT * BT

        ci = Sum{ j=1:n, ci + aji * bj}

        where A is a matrix, B is a column or transposed row vector, and C is a column vector.

        This implementation is optimal for small matrices. There is a huge performance hit when used on large matrices due to CPU cache issues.

        Parameters:
        A - A matrix that is m by n. Not modified.
        B - A vector that has length m. Not modified.
        C - A column vector that has length n. Modified.

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