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function C = accum_mask (C, Mask, accum, T, C_replace, Mask_complement)
%ACCUM_MASK2 a simpler version of GB_spec_accum_mask
% It does not handle typecasting and it assumes the identity value is zero.
% The purpose is for illustration to describe what the accum/mask operation
% does, not for actual testing. This file appears in the User Guide.
% SuiteSparse:GraphBLAS, Timothy A. Davis, (c) 2017-2022, All Rights Reserved.
% SPDX-License-Identifier: Apache-2.0
[nrows ncols] = size (C.matrix) ;
Z.matrix = zeros (nrows, ncols) ;
Z.pattern = false (nrows, ncols) ;
if (isempty (accum))
% Z = T, no accum operator
Z.matrix = T.matrix ;
Z.pattern = T.pattern ;
else
% Z = accum (C,T)
% apply the binary operator to the set intersection
p = T.pattern & C.pattern ;
Z.matrix (p) = GB_spec_op (accum, C.matrix (p), T.matrix (p)) ;
% copy entries in C but not T
p = C.pattern & ~T.pattern ;
Z.matrix (p) = C.matrix (p) ;
% copy entries in T but not C
p = T.pattern & ~C.pattern ;
Z.matrix (p) = T.matrix (p) ;
% pattern is the set union
Z.pattern = C.pattern | T.pattern ;
end
% apply the mask to the values and pattern
C.matrix = mask (C.matrix, Mask, Z.matrix, C_replace, Mask_complement) ;
C.pattern = mask (C.pattern, Mask, Z.pattern, C_replace, Mask_complement) ;
end
function C = mask (C, Mask, Z, C_replace, Mask_complement) ;
% replace C if requested
if (C_replace)
C (:,:) = 0 ; % assume identity is zero
end
if (isempty (Mask))
% implicitly, Mask = ones (size (C))
if (~Mask_complement)
% this is the default
C = Z ;
else
% note that Z need never have been computed
C = C ;
end
else
% apply the mask
if (~Mask_complement)
C (Mask) = Z (Mask) ;
else
C (~Mask) = Z (~Mask) ;
end
end
end
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