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Large, multi-dimensional, numerical arrays.

This module implements multi-dimensional arrays of integers and floating-point numbers, thereafter referred to as 'Bigarrays', to distinguish them from the standard OCaml arrays described in Array.

The implementation allows efficient sharing of large numerical arrays between OCaml code and C or Fortran numerical libraries.

The main differences between 'Bigarrays' and standard OCaml arrays are as follows:

  • Bigarrays are not limited in size, unlike OCaml arrays. (Normal float arrays are limited to 2,097,151 elements on a 32-bit platform, and normal arrays of other types to 4,194,303 elements.)
  • Bigarrays are multi-dimensional. Any number of dimensions between 0 and 16 is supported. In contrast, OCaml arrays are mono-dimensional and require encoding multi-dimensional arrays as arrays of arrays.
  • Bigarrays can only contain integers and floating-point numbers, while OCaml arrays can contain arbitrary OCaml data types.
  • Bigarrays provide more space-efficient storage of integer and floating-point elements than normal OCaml arrays, in particular because they support 'small' types such as single-precision floats and 8 and 16-bit integers, in addition to the standard OCaml types of double-precision floats and 32 and 64-bit integers.
  • The memory layout of Bigarrays is entirely compatible with that of arrays in C and Fortran, allowing large arrays to be passed back and forth between OCaml code and C / Fortran code with no data copying at all.
  • Bigarrays support interesting high-level operations that normal arrays do not provide efficiently, such as extracting sub-arrays and 'slicing' a multi-dimensional array along certain dimensions, all without any copying.

Users of this module are encouraged to do open Bigarray in their source, then refer to array types and operations via short dot notation, e.g. Array1.t or Array2.sub.

Bigarrays support all the OCaml ad-hoc polymorphic operations:

Element kinds

Bigarrays can contain elements of the following kinds:

Each element kind is represented at the type level by one of the *_elt types defined below (defined with a single constructor instead of abstract types for technical injectivity reasons).

  • since 4.07.0 Moved from otherlibs to stdlib.
type float32_elt =
  1. | Float32_elt
type float64_elt =
  1. | Float64_elt
type int8_signed_elt =
  1. | Int8_signed_elt
type int8_unsigned_elt =
  1. | Int8_unsigned_elt
type int16_signed_elt =
  1. | Int16_signed_elt
type int16_unsigned_elt =
  1. | Int16_unsigned_elt
type int32_elt =
  1. | Int32_elt
type int64_elt =
  1. | Int64_elt
type int_elt =
  1. | Int_elt
type nativeint_elt =
  1. | Nativeint_elt
type complex32_elt =
  1. | Complex32_elt
type complex64_elt =
  1. | Complex64_elt
type ('a, 'b) kind =
  1. | Float32 : (float, float32_elt) kind
  2. | Float64 : (float, float64_elt) kind
  3. | Int8_signed : (int, int8_signed_elt) kind
  4. | Int8_unsigned : (int, int8_unsigned_elt) kind
  5. | Int16_signed : (int, int16_signed_elt) kind
  6. | Int16_unsigned : (int, int16_unsigned_elt) kind
  7. | Int32 : (int32, int32_elt) kind
  8. | Int64 : (int64, int64_elt) kind
  9. | Int : (int, int_elt) kind
  10. | Nativeint : (nativeint, nativeint_elt) kind
  11. | Complex32 : (Complex.t, complex32_elt) kind
  12. | Complex64 : (Complex.t, complex64_elt) kind
  13. | Char : (char, int8_unsigned_elt) kind

To each element kind is associated an OCaml type, which is the type of OCaml values that can be stored in the Bigarray or read back from it. This type is not necessarily the same as the type of the array elements proper: for instance, a Bigarray whose elements are of kind float32_elt contains 32-bit single precision floats, but reading or writing one of its elements from OCaml uses the OCaml type float, which is 64-bit double precision floats.

The GADT type ('a, 'b) kind captures this association of an OCaml type 'a for values read or written in the Bigarray, and of an element kind 'b which represents the actual contents of the Bigarray. Its constructors list all possible associations of OCaml types with element kinds, and are re-exported below for backward-compatibility reasons.

Using a generalized algebraic datatype (GADT) here allows writing well-typed polymorphic functions whose return type depend on the argument type, such as:

let zero : type a b. (a, b) kind -> a = function
  | Float32 -> 0.0 | Complex32 -> Complex.zero
  | Float64 -> 0.0 | Complex64 -> Complex.zero
  | Int8_signed -> 0 | Int8_unsigned -> 0
  | Int16_signed -> 0 | Int16_unsigned -> 0
  | Int32 -> 0l | Int64 -> 0L
  | Int -> 0 | Nativeint -> 0n
  | Char -> '\000'
val float32 : (float, float32_elt) kind