1function w = GB_spec_reduce_to_vector (w, mask, accum, reduce, A, descriptor)
2%GB_SPEC_REDUCE_TO_VECTOR a MATLAB mimic of GrB_reduce (to vector)
3%
4% Usage:
5% w = GB_spec_reduce_to_vector (w, mask, accum, reduce, A, desc)
6%
7% Reduces a matrix to a vector
8
9% SuiteSparse:GraphBLAS, Timothy A. Davis, (c) 2017-2021, All Rights Reserved.
10% SPDX-License-Identifier: Apache-2.0
11
12%-------------------------------------------------------------------------------
13% get inputs
14%-------------------------------------------------------------------------------
15
16if (nargout > 1 || nargin ~= 6)
17    error ...
18    ('usage: c = GB_spec_reduce_to_vector (w, mask, accum, reduce, A, desc)') ;
19end
20
21% get the class of A
22if (isstruct (A))
23    aclass = A.class ;
24else
25    aclass = GB_spec_type (A) ;
26end
27
28% get the reduce operator. default type is the type of A
29if (isempty (reduce))
30    reduce = 'plus'
31end
32[reduce_op reduce_class] = GB_spec_operator (reduce, aclass) ;
33
34if (GB_spec_is_positional (reduce_op))
35    error ('reduce op must not be positional') ;
36end
37
38% get the identity
39identity = GB_spec_identity (reduce_op, reduce_class) ;
40if (isempty (identity))
41    identity = 0 ;
42end
43
44% get the input matrix
45A = GB_spec_matrix (A, identity) ;
46
47% get the input vector
48w = GB_spec_matrix (w, identity) ;
49
50% get the mask
51[C_replace Mask_comp Atrans Btrans Mask_struct] = ...
52    GB_spec_descriptor (descriptor) ;
53mask = GB_spec_getmask (mask, Mask_struct) ;
54
55%-------------------------------------------------------------------------------
56% do the work via a clean MATLAB interpretation of the entire GraphBLAS spec
57%-------------------------------------------------------------------------------
58
59% apply the descriptor to A
60if (Atrans)
61    A.matrix = A.matrix.' ;
62    A.pattern = A.pattern' ;
63end
64
65tclass = reduce_class ;
66[m n] = size (A.matrix) ;
67T.matrix = GB_spec_zeros ([m 1], tclass) ;
68T.pattern = zeros (m, 1, 'logical') ;
69T.matrix (:,:) = identity ;
70T.class = tclass ;
71
72% cast A to the type of the reduce operator, but only entries in the pattern
73
74% Note that GraphBLAS does not need the identity value to do this step.
75% Nor is the identity value specified in the GraphBLAS spec.
76% It is needed here since T is a dense column, not sparse, and the
77% implicit values need to be inserted properly.
78
79for i = 1:m
80    t = identity ;
81    for j = 1:n
82        if (A.pattern (i,j))
83            aij = GB_mex_cast (A.matrix (i,j), reduce_class) ;
84            t = GB_spec_op (reduce, t, aij) ;
85            T.pattern (i) = true ;
86        end
87    end
88    T.matrix (i) = t ;
89end
90
91%-------------------------------------------------------------------------------
92% apply the mask and accum
93%-------------------------------------------------------------------------------
94
95% w<mask> = accum (C,T): apply the accum, then mask, and return the result
96w = GB_spec_accum_mask (w, mask, accum, T, C_replace, Mask_comp, identity) ;
97
98