Arrays and Vector Operations

Code

program arrays
  implicit none

  ! 1D array
  real, dimension(10) :: a
  real :: b(5) = [1.0, 2.0, 3.0, 4.0, 5.0]

  ! 2D array
  real :: m(3, 4)

  ! Array constructor
  a = [(real(i), i=1, 10)]  ! 1.0, 2.0, ..., 10.0

  ! Whole-array operations (vectorized)
  a = a * 2.0
  a = a + b  ! must conform (here both size 10... adjust)

  ! Intrinsic functions
  print *, sum(b)        ! 15.0
  print *, maxval(b)     ! 5.0
  print *, size(b)       ! 5
  print *, sum(b, mask=b>2)  ! 12.0

  ! Array sections
  print *, b(2:4)        ! [2.0, 3.0, 4.0]
  print *, b(::2)        ! [1.0, 3.0, 5.0] (stride 2)
end program

Explanation

Fortran arrays are 1-indexed by default. Use array constructors [..] to initialize. Whole-array operations are vectorized — no explicit loops needed, and often faster. Array sections (start:end:stride) extract slices. Intrinsics like sum, maxval, minval accept masks for conditional aggregation.

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