March 11, 2026, minutes

Author: DrTimothyAldenDavis

minutes/2026-03-11.md

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+# LAGraph Working Group Meeting Minutes - March 11, 2026
+
+## Attendees
+- [x] Tim Davis
+- [x] Gabe Gomez
+- [x] Piotr Luszczek
+- [x] Michel Pelletier
+
+## Agenda and Minutes
+
+**Agenda** by Tim Davis
+
+To discuss:  replacing C pointers to array with `GrB_Vectors`, and replacing C
+input/output scalars with `GrB_Scalars`.  This will cause additional breaking
+changes in the src/ methods, if we make this change.  For example,
+`LAGr_Betweenness` takes as input `uint64_t *sources` and `int32_t ns`.  This
+could be replaced by a single `GrB_Vector sources`, as is already done in
+`LAGr_EdgeBetweennessCentrality`.  (So should `LAGr_Betweenness` be renamed to
+`LAGr_VertexBetweennessCentrality`?)
+
+Adding this `GrB_Vector` would also require a descriptor or flag to state which
+list of indices should be used for a vector v:  the indices I or values X from
+an implicit `GrB_extracTuples (I, X, v)` on the vector.
+
+**Minutes** by Tim Davis
+
+We discussed the LAGraph API, using this spreadsheet:
+https://docs.google.com/spreadsheets/d/1-WnAsmrHRYh5KQeJZzMtZYZKiKblGKYOOIkw0MdokuU/edit?usp=sharing
+
+init/finalize discussion:
+
+option 1:
+    `LAGr_Init`: needs an option to NOT initialize GraphBLAS (for symmetry)
+    `LAGr_Finalize`: needs an option to NOT finalize GraphBLAS (important)
+
+option 2:
+    `LAGr_Init`: checks if GrB has been init or not; keeps track if it called `G[rx]B_init` or not
+    `LAGr_Finalize`: only calls `GrB_finalize` if `LAGr_Init` called `G[rx]B_init`  
+
+we decided on option (2).
+
+`LAGr_Init` and `LAGr_Finalize`: need a method to ask if LAGraph has been initialized or not.
+`GrB_init` and `GrB_finalize`: need a method to ask if GraphBLAS has been finalized or not.
+
+See `MPI_Initialized` and `MPI_Finalized`
+
+Possible API: these could behave just like the MPI methods:
+
+- `GrB_Info GxB_initialized (int *flag)`
+- `GrB_Info GxB_finalized (int *flag)`
+- `GrB_Info LAGraph_Initialized (int *flag)`
+- `GrB_Info LAGraph_Finalized (int *flag)`
+
+Open question:  can we do init, call LAGraph/GrB, then finalize, then init again,
+    do more, finalize etc?  Answer: yes.
+
+GrB:
+    init:  flag to say if GrB init has been called or not
+    finalize: simply the negation of the init flag
+
+