- IMPORTANT NOTE:
- Array indices
in Fortran by default begin at
1 !!!
- Array indices can range over any interval !!! (this is a feature of Pascal)
- Array indices
in Fortran by default begin at
1 !!!
- Syntax to define an ONE-dimensional
array variable:
F77 style:
Type arrayName(size) ! Indices: 1, 2, ..., size Type arrayName(a:b) ! Indices: a, a+1, ..., b
Examples:
REAL A(5) ! A(1), A(2), A(3), A(4), A(5) REAL B(-2:2) ! B(-2), B(-1), B(0), B(1), B(2)
NOTE:
- Fortran (like C++) is optimized for
speed
- So Fortran will NOT perform run time array bound violation checks
- Fortran (like C++) is optimized for
speed
- Example Program:
(Demo above code)
- Prog file: click here
NOTE: I ran the array index in B out of bound
F90 style:
Type, DIMENSION(size) :: arrayName Type, DIMENSION(a:b) :: arrayName
Type, DIMENSION(size) :: arrayName = (/ c1, c2, ... /) Type, DIMENSION(a:b) :: arrayName = (/ c1, c2, ... /) (Last 2 syntax define initialized arrays)Examples:
REAL DIMENSION(5) :: A ! A(1), A(2), A(3), A(4), A(5) REAL DIMENSION(-2:2) :: B ! B(-2), B(-1), B(0), B(1), B(2) REAL DIMENSION(-2:2) :: C = (/ 111, 222, 333, 444, 555 /)
- Example Program:
(Demo above code)
- Prog file: click here
- Fortran was
initially designed
for
scientific computation
(Fortran = "Formula Translator")
- Fortran has
extensive support
for
arrays
(that's why this topic is so lengthy :-))
- One of the
important difference
between
Fortran and
C++ is:
- You can use
parameter variables
to
define the ranges of an
array
in F90
NOTE: you cannot use a local variable as range
(In C++ you must use constant. C++ can emulate this feature with dynamic arrays)
(This feature is not available in many languages , one language that has this feature is Ada )
- You can use
parameter variables
to
define the ranges of an
array
in F90
- Example:
SUBROUTINE f(N) IMPLICIT NONE INTEGER N REAL, DIMENSION(N) :: A !! You can define arrays using !! VARIABLES in Fortran 90.... like Ada INTEGER i DO i = 1, N A(i) = i END DO print *, A !! Print an entire array END SUBROUTINE
PROGRAM main IMPLICIT NONE CALL f(2) !! Create array of size 2 CALL f(3) !! Create array of size 3 END
- Example Program:
(Demo above code)
- Prog file:
click here
- Another program, demonstrate A(n1:n2): click here
- Prog file:
click here
-
Syntax to define a two-dimensional array in Fortran
F77 style
Type arrayName(size1, size2) Type arrayName(a1:b1, a2:b2)
Example:
REAL A(3,3) !! 3x3 matrix, indices (1,1), (1,2), etc REAL B(0:2, 0:2) !! 3x3 matrix, indices (0,0), (0,1), etc
(No demo program, I'll demo the 2-dim. array in F90 style)
F90 style
Type, DIMENSION(size1, size2) :: arrayName Type, DIMENSION(a1:b1, a2:b2) :: arrayName
Example:
REAL, DIMENSION(3, 3) :: A !! 3x3 matrix, indices (1,1), (1,2), etc REAL, DIMENSION(0:2, 0:2) :: B !! 3x3 matrix, indices (0,0), (0,1), etc REAL, DIMENSION(3, 0:2) :: C !! 3x3 matrix, indices (1,0), (1,1), etc
- Example Program:
(Demo above code)
- Prog file: click here
- Recall that:
- C++ stores an
array
as
row major:
A[0][0] A[0][1] A[0][2] A[0][3] A[0][4] A[1][0] A[1][1] A[1][2] A[1][3] A[1][4] A[2][0] A[2][1] A[2][2] A[2][3] A[2][4] stored as:
A[0][0] A[0][1] A[0][2] A[0][3] A[0][4] A[1][0] A[1][1] ... A[2][3] A[2][4]
- In contrast ,
Fortran stores an
array
as
column major:
A[0][0] A[0][1] A[0][2] A[0][3] A[0][4] A[1][0] A[1][1] A[1][2] A[1][3] A[1][4] A[2][0] A[2][1] A[2][2] A[2][3] A[2][4] stored as:
A[0][0] A[1][0] A[2][0] A[0][1] A[1][1] A[2][1] A[0][2] ... A[1][4] A[2][4]
- C++ stores an
array
as
row major:
- This little fact will help
you understand
the
DATA
block construct
- Fortran has a funny
DATA block
construct that you can use to
initialize variables
- It is commonly used to
initialize array variables
- DATA block syntax:
DATA varName / val1, val2, .... /
Example:
REAL A(5) REAL B(2, 3) DATA A / 1, 2, 3, 4, 5 / DATA B / 1, 2, 3, 4, 5, 6 / ! NOTE: Column major !!!
Result: A(1) = 1, A(2) = 2, A(3) = 3, A(4) = 4, A(5) = 5 B(1,1) = 1, B(1,2) = 3, B(1,3) = 5 B(2,1) = 2, B(2,2) = 4, B(2,3) = 6
- Example Program:
(Demo above code)
- Prog file: click here