Invalid vector size bug during Tree-HDagg partitioning for certain input matrices

Bug description

The SpTrSv_LL_Tree_HDAGG case in SpTRSV_runtime.cpp example leads to error for certain input matrices:

Running LL HDAGG with BIN Code with #core: 4 - The runtime:7.7951e-05
core: 4; bin: 1
Compute DAG
terminate called after throwing an instance of 'std::length_error'
  what():  cannot create std::vector larger than max_size()
Aborted (core dumped)

This happens, for example, with input matrix A = random_square_sparse(200, 0.5, 1.0, 2U);, and with Metis reordering disabled. Depending on the random parameters, some matrices fail while others run fine.

Locating bug

The error occurs inside the HDAGG function, at the following call with invalid vector size nlevels = -1: https://github.com/sympiler/aggregation/blob/da293bb1d1060bc390ad785978f8452943a8909c/src/hdagg/hdagg.cpp#L663

The invalid value -1 is returned by the build_levelSet_CSC function at line 44: https://github.com/sympiler/aggregation/blob/da293bb1d1060bc390ad785978f8452943a8909c/src/hdagg/hdagg.cpp#L41-L64

When error occurs, the variable state is cur_level == n == 2, then -1 is returned. Moreover, the code in line 45~64 is placed after return so will never get executed, so I guess some logic must be wrong here. The assert at line 42 should probably be enabled?

Steps to reproduce

Modify SpTRSV_runtime.cpp with the following input matrix:

n = 200;
double density = 0.5;
matrix_name = "Random_" + std::to_string(n);
A = random_square_sparse(n, density, 1.0, 2U);

...
// disable METIS
#undef METIS
#ifdef METIS
...
#else
  // avoid name conflict with another `tmp` variable later
  CSC *tmp_csc =
      make_half(Lower_A_CSC->n, Lower_A_CSC->p, Lower_A_CSC->i, Lower_A_CSC->x);
  delete Lower_A_CSC;
  Lower_A_CSC = tmp_csc;
  Lower_A_CSR = csc_to_csr(Lower_A_CSC);
#endif

I can also send a draft PR to show such bug, and a parameterized unit test to sweep over various input matrices (update: see #10).

Then, build and run:

cmake -B build_debug -DCMAKE_BUILD_TYPE=Debug
cmake --build build_debug --target Hdagg_SpTRSV
./build_debug/example/Hdagg_SpTRSV   # get bug

Deeper look with GDB:

gdb ./build_debug/example/Hdagg_SpTRSV
(check state of `n` before entering loop)
break src/hdagg/hdagg.cpp:28
(check state of `cur_level` before returning -1)
break src/hdagg/hdagg.cpp:44

(the first break point is inside `SpTrSv_LL_HDAGG` case, not yet to `SpTrSv_LL_Tree_HDAGG`, so no bug)
run
print n
(n equals 200 for this input)

(the second break point is inside the buggy `SpTrSv_LL_Tree_HDAGG`)
c
print n
(n equals 2 because ngroups is used as first argument of HDAGG() function)

(the third break point is just before returning -1)
print cur_level
(cur_level equals 2, so -1 is returned as result of build_levelSet_CSC() function)

c
(crashes when creating a vector of size -1)

sympiler / aggregation