findmax and findmin built-ins about graphblas HOT 3 OPEN

Let's keep this open so I don't forget. Creating semirings based on an index-binary operator (which would have access to the values aik, bkj, and the indices i,k,j) is very important. It will be a lot of work, but it would not require a JIT to get important cases to work with high performance.

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It's currently not possible to create a user-defined positional binary op. Internally, built-in ops "can do anything" ... I just have to write the code to do it, and none of my specialized positional binary ops can do this. There is no function signature that handles this; my positional binary ops are GrB_BinaryOp objects.

There is a new GrB_IndexUnaryOp in the spec, which computes z = f (aij, i, j, thunk). It's like a selectop, but it can be used in more than just GrB_select. It can be used in GrB_apply as well.

It would be possible to consider an extension to this idea, a GxB_IndexBinaryOp, which would compute z = f (a_ia_ja, ia, ja, b_ib_jb, ib,jb, thunk), where A(ia,ja) is one entry and B(ib,jb) is another. This function signature could be used to return z as a pair of entries: (value,k) where you'd use k = ja or k = ib. Then a user-defined max monoid could be considered that operated on the user-data type (value,int64 k).

The GrB_Semiring would have to be extended so it can handle this GxB_BinaryIndexOp as the multiplicative operator.

This would be quite a lot of work to implement, however. All my extensive AxB kernels would have to change to accomodate this new kind of op, and the change is substantial.

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Closing since this will be taken care of eventually by JIT and possibly Enzyme.

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