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Mojo struct

ArgMin

struct ArgMin[dtype: DType, W: Int = simd_width_of[dtype]()]

Argmin reduction monoid: mirrors ArgMax with </ge comparison (see ArgMax for the algorithm + design notes).

Parameters​

  • ​dtype (DType): The value dtype.
  • ​W (Int): SIMD width of the per-lane accumulator. Same GPU/CPU default rationale as ArgMax.

Fields​

  • ​best (Scalar[dtype]): Final scalar best value.
  • ​best_idx (Int): Final scalar best index.
  • ​acc_values (SIMD[dtype, W]): Per-lane running min during SIMD-wide tile accumulation.
  • ​acc_indices (SIMD[DType.int64, W]): Per-lane axis indices corresponding to acc_values.

Implemented traits​

AnyType, Copyable, ImplicitlyCopyable, ImplicitlyDeletable, Movable, ReduceOp, RegisterPassable, TrivialRegisterPassable

comptime members​

Single​

comptime Single = ArgMin[dtype, Int(1)]

width​

comptime width = W

Methods​

__init__​

def __init__() -> Self

Identity: best = +inf/MAX, best_idx = Int.MAX, SIMD accs at the same identity.

__getitem__​

def __getitem__(self, j: Int) -> Self.Single

Returns lane j as a width-1 monoid.

Returns:

Self.Single

__setitem__​

def __setitem__(mut self, j: Int, s: ArgMin[dtype, Int(1)])

Writes width-1 monoid s into lane j.

accumulate​

def accumulate[val_dtype: DType, w: Int](mut self, val: SIMD[val_dtype, w], idx: SIMD[DType.int64, w] = 0)

Folds a SIMD tile via lane-wise compare-and-select. Mirrors ArgMax.accumulate with the >= rule: padded value lanes +inf/MAX, padded index lanes Int64.MAX, so they always lose to any real candidate. ge (not gt) preserves the lower-idx tie-break. idx is the scaffolder-built per-lane axis-position vector — the monoid never adds an iota.

Parameters:

  • ​val_dtype (DType): The tile's source dtype.
  • ​w (Int): SIMD width of the tile.

Args:

join​

def join(mut self, other: Self)

Sequential combine. Element-wise SIMD merge of the acc; scalar merge of the (best, best_idx) tail. Tie-symmetric: when values tie, the smaller index wins. Mirrors ArgMax.join with < instead of >.

Args:

  • ​other (Self): The state to combine into self.

reduce​

def reduce(self) -> Self.Single

SIMD-tree collapse (faster than the default lane-fold for a value+index select): min value in lane 0, lowest index among the min lanes. join_parallel folds lane 0 into (best, best_idx).

Returns:

Self.Single

join_parallel​

def join_parallel[R: Reducer](mut self, reducer: R)

Folds the within-thread acc at lane 0 into the scalar (best, best_idx), resets the SIMD acc, combines across participants via reducer.generic, and leaves the winning index in acc_indices[0]. Mirrors ArgMax.join_parallel with the < tie-break. Works at any W (collapse pre-reduces to lane 0 when W > 1).

Parameters:

  • ​R (Reducer): The parallel reducer.

Args:

  • ​reducer (R): The reducer instance.

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