% Run the GraphBLAS demo2

% SuiteSparse:GraphBLAS, Timothy A. Davis, (c) 2017-2020, All Rights Reserved.
% http://suitesparse.com   See GraphBLAS/Doc/License.txt for license.

gbdemo2
 GBDEMO2 Extreme performance differences: GraphBLAS vs MATLAB.
 
  Usage:
 
        gbdemo2             % uses a default bnz = 6000
        gbdemo2 (20000)     % uses bnz = 20000
 
  The GraphBLAS operations used in gbdemo are perhaps 3x to 50x
  faster than the corresponding MATLAB operations, depending on how
  many cores your computer has.  Here's an example where GraphBLAS is
  asymptotically far faster than MATLAB R2019a: a simple assignment
  for a large matrix C:
 
        C(I,J) = A
 
  The matrix C is constructed via C = kron (B,B) where nnz (B) is
  roughly the bnz provided on input (with a default of bnz = 6000),
  so that C will have about bnz^2 entries, or 36 million by default.
  I and J are chosen randomly, and A is 5000-by-5000.
 
  When the problem becomes large, MATLAB will take a very long time.
  If you have enough memory, and want to see higher speedups in
  GraphBLAS, increase bnz (and be prepared to wait even longer).
  With the default bnz = 6000, this test takes about 4GB of RAM.
 
  On my Dell XPS 4-core laptop (Intel(R) Core(TM) i7-8565U, 16GB
  RAM), using MATLAB R2019a, when C becomes 9 million by 9 million,
  the computation C(I,J)=A for MATLAB matrices C, I, J, and A takes
  several minutes, whereas GraphBLAS takes less than a second, or
  about 500x faster than MATLAB.  On a desktop with an Intel(R)
  Xeon(R) CPU E5-2698 v4 @ 2.20GHz with 20 hardware cores, the
  speedup over MATLAB is even more dramatic (up to 2,660x has been
  observed).
 
  See also GrB.assign, subsasgn.


# of threads used in GraphBLAS: 8


C(I,J)=A where C is 1 million -by- 1 million
with 35.7126 million entries:

    A is 5000-by-5000 with 49954 entries
    setup time:     0.261989 sec
    GraphBLAS time: 0.272427 sec
    Starting MATLAB ... please wait ... 
    MATLAB time:    0.349314 sec
    Speedup of GraphBLAS over MATLAB: 1.28223
    check time:     0.260897 sec
    all tests passed

C(I,J)=A where C is 4 million -by- 4 million
with 35.8202 million entries:

    A is 5000-by-5000 with 49954 entries
    setup time:     0.319877 sec
    GraphBLAS time: 0.333537 sec
    Starting MATLAB ... please wait ... 
    MATLAB time:    0.345186 sec
    Speedup of GraphBLAS over MATLAB: 1.03493
    check time:     0.297323 sec
    all tests passed

C(I,J)=A where C is 9 million -by- 9 million
with 35.928 million entries:

    A is 5000-by-5000 with 49954 entries
    setup time:     0.356083 sec
    GraphBLAS time: 0.391448 sec
    Starting MATLAB ... please wait ... 
    MATLAB time:    187.06 sec
    Speedup of GraphBLAS over MATLAB: 477.866
    check time:     0.292156 sec
    all tests passed

C(I,J)=A where C is 16 million -by- 16 million
with 35.916 million entries:

    A is 5000-by-5000 with 49954 entries
    setup time:     0.40299 sec
    GraphBLAS time: 0.446623 sec
    Starting MATLAB ... please wait ... 
    MATLAB time:    199.164 sec
    Speedup of GraphBLAS over MATLAB: 445.934
    check time:     0.492775 sec
    all tests passed

C(I,J)=A where C is 25 million -by- 25 million
with 35.964 million entries:

    A is 5000-by-5000 with 49954 entries
    setup time:     0.464605 sec
    GraphBLAS time: 0.395374 sec
    Starting MATLAB ... please wait ... 
    MATLAB time:    230.122 sec
    Speedup of GraphBLAS over MATLAB: 582.036
    check time:     0.369713 sec
    all tests passed

C(I,J)=A where C is 36 million -by- 36 million
with 35.976 million entries:

    A is 5000-by-5000 with 49954 entries
    setup time:     0.510898 sec
    GraphBLAS time: 0.681213 sec
    Starting MATLAB ... please wait ... 
    MATLAB time:    251.809 sec
    Speedup of GraphBLAS over MATLAB: 369.649
    check time:     0.416664 sec
    all tests passed