Source file: polyminmax.fut

Polymorphic minimum and maximum

Futhark provides built-in functions for computing the minimum and maximum element of arrays of built-in types. The following functions are generic implementations that work for any type, as long as you provide a comparison operator.

def minimum [n] 't ((<=): t -> t -> bool) (a: [n]t) : t =
  reduce (\x y -> if x <= y then x else y) a[0] a

def maximum [n] 't ((<=): t -> t -> bool) (a: [n]t) : t =
  minimum (flip (<=)) a

We can instantiate them to obtain the normal functions.

def minimum_i32 = minimum (i32.<=)

> minimum_i32 [1,2,3,-4,5]

-4i32

The functions above are not perfect, as they require the element to be non-empty. One could conceive of variants that use option types to handle empty arrays. However, it is most efficient if we can provide a sensible neutral/dummy element for the reduction.

Polymorphic minimum and maximum

See also