# At_mul_B

At_mul_B(A, B)

For matrices or vectors \$A\$ and \$B\$, calculates \$Aáµ€â‹…B\$

## Examples

``````julia> A = [1 2 3; 4 5 6];
julia> B = [7, 8, 9];
julia> At_mul_B(A, B)
2-element Array{Int64,1}:
50
122``````

This example calculates the dot product of the transpose of matrix `A` and vector `B`. The result is an array of length 2.

``````julia> A = [1 2; 3 4; 5 6];
julia> B = [7 8; 9 10];
julia> At_mul_B(A, B)
2×2 Array{Int64,2}:
46   52
64   72``````

In this example, `A` is a matrix and `B` is also a matrix. The function `At_mul_B` calculates the matrix product of the transpose of `A` and `B`, resulting in a 2x2 matrix.

Common mistake example:

``````julia> A = [1 2 3; 4 5 6];
julia> B = [7, 8];
julia> At_mul_B(A, B)
ERROR: DimensionMismatch("matrix A has dimensions (2, 3), vector B has length 2")``````

In this example, the dimensions of `A` and `B` are incompatible for matrix multiplication. Ensure that the number of columns in `A` matches the length of `B` to avoid this error.