% 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
maxNumCompThreads ('automatic') ;
GrB.clear ;

gbdemo2
 GBDEMO2 Extreme performance differences: GraphBLAS vs MATLAB.
 
  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: 4


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:     0.500407 sec
    GraphBLAS time: 0.480083 sec
    Starting MATLAB ... please wait ... 
    MATLAB time:    0.324153 sec
    Speedup of GraphBLAS over MATLAB: 0.675202
    check time:     0.367465 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:     0.368867 sec
    GraphBLAS time: 0.377529 sec
    Starting MATLAB ... please wait ... 
    MATLAB time:    0.356893 sec
    Speedup of GraphBLAS over MATLAB: 0.945339
    check time:     0.297686 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:     0.422128 sec
    GraphBLAS time: 0.457822 sec
    Starting MATLAB ... please wait ... 
    MATLAB time:    188.43 sec
    Speedup of GraphBLAS over MATLAB: 411.579
    check time:     0.309589 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:     0.515202 sec
    GraphBLAS time: 0.560895 sec
    Starting MATLAB ... please wait ... 
    MATLAB time:    209.334 sec
    Speedup of GraphBLAS over MATLAB: 373.213
    check time:     0.405357 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:     0.541219 sec
    GraphBLAS time: 0.561812 sec
    Starting MATLAB ... please wait ... 
    MATLAB time:    257.241 sec
    Speedup of GraphBLAS over MATLAB: 457.877
    check time:     0.416152 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:     0.569174 sec
    GraphBLAS time: 0.849047 sec
    Starting MATLAB ... please wait ... 
    MATLAB time:    258.647 sec
    Speedup of GraphBLAS over MATLAB: 304.632
    check time:     0.491769 sec
    all tests passed