Fortranordered

Fortranordered refers to the memory layout of multi-dimensional arrays that follows the Fortran convention of storing data in column-major order. In this arrangement, elements within each column are stored contiguously in memory, and columns themselves appear one after another. This contrasts with row-major order, used by C and many other environments, where elements within each row are stored contiguously.

The term is commonly encountered in numerical computing contexts where interoperability with Fortran libraries or legacy code is important. Many languages and libraries provide ways to request Fortran-ordered storage, or to detect it, via array flags or layout parameters. For example, in NumPy, an array can be Fortran-ordered by creating it with order='F' or converting with asfortranarray, and its memory layout can be inspected via flags such as F_CONTIGUOUS.

Choosing Fortran-ordered storage affects performance characteristics due to cache locality and the way multidimensional indices map to linear memory addresses. When performing operations that traverse arrays column by column, Fortran order can be advantageous, especially for environments where column-major storage is natural (such as Fortran and many linear algebra routines). Conversely, interacting with row-major systems might require transpositions or data copies to avoid inefficient striding.

In practice, whether an array is Fortran-ordered is a property of its memory layout, not a separate data type. It is one of several layouts a numerical program may use, and developers often need to consider it for interoperability with libraries, performance optimization, and correct indexing semantics.