File Exchange ## Dot product of two N-dimensional arrays.

version 1.0.0.0 (2.51 KB) by Xiaodong

### Xiaodong (view profile)

DOT3(A, B) returns their scalar product, where A and B are arbitrary arrays with arbitrary sizes.

Updated 20 May 2013

%DOT3 Vector dot product.
% This function exploits the MULTIPROD engine (MATLAB Central, file
% #8773), which enables multiple products and array expansion (AX).
%
% When A and B are vectors (e.g. P×1, 1×P, or 1×1×P arrays):
%
% C = DOT3(A, B) returns their scalar product. A and B must have the
% same length. If A and B are both column vectors, DOT3(A, B) is the
% same as (A.') * B. Note that: If NDIMS(A) == 2 and NDIMS(B) == 2,
% DOT3(A, B) is not equivalent to DOT(A, B) or DOT2(A,B) (File ID: #8782). DOT(A, B)
% or DOT2(A, B) applies a complex conjugate on the first parameter A,
% but DOT3(A, B) does not apply the complex conjugate on A.
%
% More generally, when A and B are arrays of any size containing one or
% more vectors:
%
% C = DOT3(A, B) is equivalent to C = DOT3(A, B, IDA, IDB), where
% IDA and IDB are the first non-singleton dimensions of A and B,
% respectively.
%
% C = DOT3(A, B, DIM) is equivalent to C = DOT3(A, B, IDA, IDB),
% where IDA = IDB = DIM.
%
% C = DOT3(A, B, IDA, IDB) returns the scalar products between the
% vectors contained in A along dimension IDA and those contained in B
% along dimension IDB. These vectors must have the same length
% P = SIZE(A,IDA) = SIZE(B,IDB). A and B are viewed as "block
% arrays". IDA and IDB are referred to as their "internal dimensions"
% (IDs). For instance, a 5×6×2 array may be viewed as an array
% containing twelve 5-element blocks. In this case, its size is
% denoted by (5)×6×2, and its ID is 1. Since AX is enabled, A and B
% may have different size, and IDA may not coincide with IDB (see
% MULTIPROD).
%
% C = DOT3(A, B, IDA, IDB) calls C = MULTIPROD(CONJ(A), B, IDA, IDB)
% (MATLAB Central, file #8773), which virtually turns the vectors
% found in CONJ(A) and B into 1×P and P×1 matrices, respectively,
% then returns their products.
%
% Input and output format (see MULTIPROD, syntax 4b):
% Array Block size Internal dimension
% -------------------------------------------
% A P (1-D) IDA
% B P (1-D) IDB
% C 1 (1-D) MAX(IDA, IDB)
% -------------------------------------------
%
% Examples:
% If A and B are both (5)×6×2 arrays of vectors,
% C = DOT3(A, B) is a (1)×6×2 array of scalars.
%
% A single vector B multiplies thirty vectors contained in A:
% If A is .............. a 5×6×(3) array of 30 vectors,
% and B is .............. a (3)×1 vector,
% C = DOT3(A, B, 3, 1) is a 5×6×(1) array of 30 scalars.
%
% REJECTION, MULTIPROD, TESTDOT2.

% \$ Version: 1.0 \$
% Code is modified by Xiaodong Qi (i2000s# hotmail.com) from DOT2 (dot2 is
% written by Paolo de Leva (IUSM, Rome, IT) 2009 Jan, File ID: #8782) to
% make a good match to another common definition of dot products.
% May 17, 2013.