graphblas_demo2
Date: 2021-11-13

    % Run the GraphBLAS demo2

    % SuiteSparse:GraphBLAS, Timothy A. Davis, (c) 2017-2021, All Rights Reserved.
    % SPDX-License-Identifier: Apache-2.0

    % reset to the default number of threads
    clear all
    ncores = demo_nproc ;
    GrB.clear ;

    gbdemo2

     GBDEMO2 Extreme performance differences: GraphBLAS vs built-in methods.

      Usage:

            gbdemo2             % uses a default bnz = 6000
            gbdemo2 (20000)     % uses bnz = 20000

      Many of 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: 20

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

        A is 5000-by-5000 with 49947 entries
        setup time:     0.415349 sec
        GraphBLAS time: 0.264042 sec
        Starting MATLAB ... please wait ...
        MATLAB time:    0.472303 sec
        Speedup of GraphBLAS over MATLAB: 1.78874
        check time:     0.353221 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 49947 entries
        setup time:     0.454911 sec
        GraphBLAS time: 0.209247 sec
        Starting MATLAB ... please wait ...
        MATLAB time:    0.482239 sec
        Speedup of GraphBLAS over MATLAB: 2.30464
        check time:     0.239005 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 49947 entries
        setup time:     0.536653 sec
        GraphBLAS time: 0.271364 sec
        Starting MATLAB ... please wait ...
        MATLAB time:    197.428 sec
        Speedup of GraphBLAS over MATLAB: 727.538
        check time:     0.280854 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 49947 entries
        setup time:     0.615692 sec
        GraphBLAS time: 0.328814 sec
        Starting MATLAB ... please wait ...
        MATLAB time:    214.611 sec
        Speedup of GraphBLAS over MATLAB: 652.683
        check time:     0.302003 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 49947 entries
        setup time:     0.684777 sec
        GraphBLAS time: 0.295649 sec
        Starting MATLAB ... please wait ...
        MATLAB time:    237.231 sec
        Speedup of GraphBLAS over MATLAB: 802.407
        check time:     0.340822 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 49947 entries
        setup time:     0.77091 sec
        GraphBLAS time: 0.458453 sec
        Starting MATLAB ... please wait ...
        MATLAB time:    263.984 sec
        Speedup of GraphBLAS over MATLAB: 575.815
        check time:     0.386426 sec
        all tests passed