## Class MatrixVectorMult

- java.lang.Object
- org.ejml.alg.dense.mult.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 Summary

Constructors Constructor and Description **MatrixVectorMult**()

### Method Summary

Methods Modifier and Type Method and Description `static void`

**mult**(RowD1Matrix64F a, D1Matrix64F b, D1Matrix64F c)Performs a matrix vector multiply.

c = A * b

and

c = A * b^{T}

c_{i}= Sum{ j=1:n, a_{ij}* b_{j}}

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

**multAdd**(RowD1Matrix64F A, D1Matrix64F B, D1Matrix64F C)Performs a matrix vector multiply.

C = C + A * B

or

C = C + A * B^{T}

c_{i}= Sum{ j=1:n, c_{i}+ a_{ij}* b_{j}}

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

**multAddTransA_reorder**(RowD1Matrix64F A, D1Matrix64F B, D1Matrix64F C)An alternative implementation of`multAddTransA_small(org.ejml.data.RowD1Matrix64F, org.ejml.data.D1Matrix64F, org.ejml.data.D1Matrix64F)`

that performs well on large matrices.`static void`

**multAddTransA_small**(RowD1Matrix64F A, D1Matrix64F B, D1Matrix64F C)Performs a matrix vector multiply.

C = C + A^{T}* B

or

C = C^{T}+ A^{T}* B^{T}

c_{i}= Sum{ j=1:n, c_{i}+ a_{ji}* b_{j}}

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

**multTransA_reorder**(RowD1Matrix64F A, D1Matrix64F B, D1Matrix64F C)An alternative implementation of`multTransA_small(org.ejml.data.RowD1Matrix64F, org.ejml.data.D1Matrix64F, org.ejml.data.D1Matrix64F)`

that performs well on large matrices.`static void`

**multTransA_small**(RowD1Matrix64F A, D1Matrix64F B, D1Matrix64F C)Performs a matrix vector multiply.

C = A^{T}* B

where B is a column vector.

or

C = A^{T}* B^{T}

where B is a row vector.

### Method Detail

#### mult

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

Performs a matrix vector multiply.

c = A * b

and

c = A * b^{T}

c_{i}= Sum{ j=1:n, a_{ij}* b_{j}}

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 * B^{T}

c_{i}= Sum{ j=1:n, c_{i}+ a_{ij}* b_{j}}

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 = A^{T}* B

where B is a column vector.

or

C = A^{T}* B^{T}

where B is a row vector.

c_{i}= Sum{ j=1:n, a_{ji}* b_{j}}

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.

#### multTransA_reorder

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

An alternative implementation of`multTransA_small(org.ejml.data.RowD1Matrix64F, org.ejml.data.D1Matrix64F, org.ejml.data.D1Matrix64F)`

that performs well on large matrices. There is a relative performance hit when used on small matrices.- 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.

#### multAddTransA_small

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

Performs a matrix vector multiply.

C = C + A^{T}* B

or

C = C^{T}+ A^{T}* B^{T}

c_{i}= Sum{ j=1:n, c_{i}+ a_{ji}* b_{j}}

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.

#### multAddTransA_reorder

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

An alternative implementation of`multAddTransA_small(org.ejml.data.RowD1Matrix64F, org.ejml.data.D1Matrix64F, org.ejml.data.D1Matrix64F)`

that performs well on large matrices. There is a relative performance hit when used on small matrices.- 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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