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function [S,p] = GB_spec_build (I, J, X, nrows, ncols, op, order, sclass)
%GB_SPEC_BUILD a MATLAB version of GrB_Matrix_build and GrB_vector_build
%
% Usage:
% [S p] = GB_spec_build (I, J, X, nrows, ncols, op, order)
%
% GB_spec_build builds a full matrix S, mimicing GB_mex_Matrix_build but in
% almost pure MATLAB. This function is very slow since it creates a dense
% matrix instead of a sparse one. It is meant only as an executable version of
% the GraphBLAS spec. It cannot operate purely in MATLAB, however, because the
% casting and operator rules in MATLAB differ from the C-style casting and
% operator rules GraphBLAS. In MATLAB, adding two int8 values 120 + 30 results
% in 127; since 150 is larger than the max int8 value of 127, the result is
% that max value. In C, the result wraps around, modulo 256, to be -106.
%
% S is returned as a struct, with S.matrix being the matrix, S.class the class,
% and S.pattern the nonzero pattern of S.
%
% I: row indices. Indices are zero-based, just like GB_mex_Matrix_build.
%
% optional arguments:
% J: column indices. Default J is a vector of all zeros, for building a column
% vector.
% X: numerical values, with MATLAB class logical, any integer, single, or
% double. I, J, and X must have the same number of entries.
% Default X is a logical vector of all true.
% nrows: number of rows of S. Default is nrows = max (I) + 1 ;
% ncols: number of cols of S. Default is ncols = max (J) + 1 ;
% op: binary operator z=f(x,y) for assembling duplicates. See
% GB_spec_operator. The GraphBLAS spec requires op to be associative
% (min, max, plus, or times) but any binary operator with x,y,z
% types the same will work; see the 'order' parameter.
% order: 'natural', or 'random'. Default is 'natural'.
% The GraphBLAS spec does not state what order the duplicates are
% assembled. It only guarantees the result if op is associative. The
% 'natural' order sums them up in the order they appear in [I,J,X], and
% this is what GB_mex_Matrix_build does. To check the results against
% any possible order, use 'random', which sums them up in a random
% order. The results of 'natural' and 'random' will differ if op is not
% associative. With floating-point values, roundoff may vary slightly,
% which should be acceptable. If the results differ greatly then the
% problem is very ill-conditioned. The output p returns the ordering
% used to assemble the entries, a permutation of 1:length(X).
%
% Use an empty value ([ ] or '') to obtain the default value for optional
% parameters, or pass fewer inputs. For exampe S = GB_spec_build (I, J, X,
% nrows, ncols) uses defaults for op, and order, but not X, nrows and ncols.
% SuiteSparse:GraphBLAS, Timothy A. Davis, (c) 2017-2020, All Rights Reserved.
% http://suitesparse.com See GraphBLAS/Doc/License.txt for license.
%-------------------------------------------------------------------------------
% get inputs
%-------------------------------------------------------------------------------
if (nargout > 2 || nargin < 1 || nargin > 8)
error ('usage: [S p] = GB_spec_build (I, J, X, nrows, ncols, op, order, sclass)') ;
end
% get I
nnz = length (I) ;
% get J
if (nargin < 2)
J = [ ] ;
end
if (isempty (J))
J = zeros (nnz, 1) ;
end
if (nnz ~= length (J))
error ('I and J must have the same size') ;
end
% get X
if (nargin < 3)
X = [ ] ;
end
if (isempty (X))
X = ones (nnz, 1, 'logical') ;
end
if (nnz ~= length (X))
error ('I and X must have the same size') ;
end
% get the number of rows
if (nargin < 4)
nrows = [ ] ;
end
if (isempty (nrows))
nrows = max (I) + 1 ;
end
% get the number of cols
if (nargin < 5)
ncols = [ ]
end
if (isempty (ncols))
ncols = max (J) + 1 ;
end
% get the op
if (nargin < 6)
op = [ ] ;
end
if (isempty (op))
op = 'plus' ;
end
[opname optype ztype xtype ytype] = GB_spec_operator (op, GB_spec_type (X)) ;
assert (isequal (ztype, xtype)) ;
assert (isequal (ztype, ytype)) ;
% get the ordering
if (nargin < 7)
order = '' ;
end
%-------------------------------------------------------------------------------
% do the work via a clean MATLAB interpretation of the entire GraphBLAS spec
%-------------------------------------------------------------------------------
% sort or randomize the tuples
if (isequal (order, 'random'))
% the GraphBLAS spec allows for any ordering
p = randperm (nnz) ;
else
% the 'natural' ordering is used in this implementation of GrB_Matrix_build
[~, p] = sortrows ([J I (1:nnz)']) ;
end
I = I (p) ;
J = J (p) ;
X = X (p) ;
% initialize the matrix S and its pattern
S.matrix = GB_spec_zeros ([nrows ncols], optype) ;
S.pattern = false (nrows, ncols) ;
S.class = optype ;
% assemble the tuples into S
for t = 1:nnz
i = 1 + I (t) ; % convert from 0-based GraphBLAS to 1-based MATLAB
j = 1 + J (t) ;
if (~S.pattern (i,j))
% first time S(i,j) is modified: cast x into S
S.matrix (i,j) = GB_mex_cast (X (t), optype) ;
S.pattern (i,j) = true ;
else
% a duplicate entry to be assembled with the operator op
% cast x into the class of S and the operator
x = GB_mex_cast (X (t), optype) ;
% apply the operator, result is of class optype
S.matrix (i,j) = GB_spec_op (op, S.matrix (i,j), x) ;
end
end
% get the sclass
if (nargin < 8)
sclass = optype ; % default is optype
end
% typecast S into the desired class
if (~isequal (optype, sclass))
S.matrix = GB_mex_cast (S.matrix, sclass) ;
S.class = sclass ;
end
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