Array Attributes

In F90 the following terminology is used:

• Size = total number of elements. Both A and B have size = 6.
• Rank = number of dimensions. In F90 the rank should be less than or equal to 7. A has rank 1, B has rank 2.
• Extent = number of elements in each dimension. A has extent 6, B has extents 2 and 3. Note that the extent can be ZERO (in this case the expressions involving the array are simply ignored).
• Bounds = upper and lower limits of indices; by default, they are taken 1:Extent. E.g: A index varies between 1 and 6, while B indices vary between 1 and 2, and 1 and 3 respectively. These bounds can be changed using declarations of the form

  real, dimension(-2:3)       :: a
  real, dimension(-10:-9,5:7) :: b
  real :: a(-2:3), b(-10:-9,5:7)   ! shorthand form
  

• Shape = rank and extents. E.g: A has shape (/6/) and B has shape (/2,3/).

F90 provides a number of intrinsic functions that ``inquire'' the arrays about their attributes and status. These intrinsics are useful inside procedure bodies; for example we can obtain the dimensions (extents) of an input array argument without explicitly requiring them in the argument list. The inquiry intrinsic functions may return the lower and the upper subscript bounds (LBOUND and UBOUND), the shape (SHAPE) and the size (SIZE) of an array.

For example