Swap

This subroutine can swap two integer (scalar, vector, matrix) and two real numbers (scalar, vector, matrix). It can also swap the dimension of a Fortran array.

note

We can use this method for swapping two variables a and b, where a and b can be scalar, vector or matrix of Fortran intrinsic types.

note

We can also use this method for swaping the dimension of a multi-dimension array. For example, consider an array b(3,4), we can interchange the row and column dimension (i.e., transpose operation) by using swap.

Interface 1

܀ Interface
️܀ See example
↢

INTERFACE
  MODULE PURE SUBROUTINE Swap(a, b, i1, i2)
    REAL(Real32), ALLOCATABLE, INTENT(INOUT) :: a(:, :)
      !! the returned array
    REAL(Real32), INTENT(IN) :: b(:, :)
      !! input array, it will be untouched
    INTEGER(I4B), INTENT(IN) :: i1
      !! index 1 is Swapped with index `i1`
      !! make sure i1 is lesser than or equal to 2
    INTEGER(I4B), INTENT(IN) :: i2
      !! index 2 is Swapped with index `i2`
      !! make sure i2 is less than or equal to 2
  END SUBROUTINE Swap
END INTERFACE

Swap two scalars.

PROGRAM main
    USE easifemBase
    IMPLICIT NONE
    REAL( DFP ), ALLOCATABLE :: a2(:,:), b2(:,:), a3(:,:,:), b3(:,:,:), &
      & a4(:,:,:,:), b4(:,:,:,:)

Make a random matrix and display it.

CALL Reallocate( b2, 4, 3 )
CALL RANDOM_NUMBER(b2)

Make another matrix a so that we can swap the indices of b and SAVE it in a.

In this swap we are using:

i1=1
i2=2

which means a=b.

CALL SWAP(a=a2,b=b2,i1=1,i2=2)
CALL OK( ALL( a2 .approxeq. b2 ), "swap"  )

Now let us use

i1=2
i2=1

which will produce a=transpose(b).

CALL SWAP(a=a2,b=b2,i1=2,i2=1)
CALL OK( ALL( a2 .approxeq. TRANSPOSE(b2) ), "swap"  )

Let us see what happens when i1=1, i2=1. Actually, it will DO nothing but a=b.

CALL SWAP(a=a2,b=b2,i1=1,i2=1)
CALL OK( ALL( a2 .approxeq. b2), "swap"  )

We DO not indend to USE swap for two-dimensional arrays, because we already have transpose FUNCTION for doing the same. The purpose was to check that algorithm works.

END PROGRAM main

Interface 2

܀ Interface
️܀ See example
↢

INTERFACE
  MODULE PURE SUBROUTINE Swap(a, b, i1, i2, i3)
    REAL(Real32|Real64), ALLOCATABLE, INTENT(INOUT) :: a(:, :, :)
    !! the returned array
    REAL(Real32|Real64), INTENT(IN) :: b(:, :, :)
    !! input array, it will be untouched
    INTEGER(I4B), INTENT(IN) :: i1
    !! index 1 is Swapped with index `i1`
    !! make sure i1 is lesser than or equal to 3
    INTEGER(I4B), INTENT(IN) :: i2
    !! index 2 is Swapped with index `i2`
    !! make sure i2 is less than or equal to 3
    INTEGER(I4B), INTENT(IN) :: i3
    !! index 3 is Swapped with index `i3`
    !! make sure i3 is less than or equal to 3
  END SUBROUTINE Swap
END INTERFACE

This example shows the usage of Swap method.

PROGRAM main
  USE easifemBase
  IMPLICIT NONE
  REAL( DFP ), ALLOCATABLE :: a2(:,:), b2(:,:), a3(:,:,:), b3(:,:,:), &
    & a4(:,:,:,:), b4(:,:,:,:)

Now let us USE swap for rank 3 Fortran array. But, first generate a rank 3 arrays, and display its content.

CALL Reallocate(b3, 2,3,2)
CALL Random_NUMBER(b3)
CALL Display(MdEncode(b3), "b3 = ")

b3 = ( :, :, 1 ) =


0.85128	7.97914E-03	0.12877
0.61923	2.30844E-02	0.67707

( :, :, 2 ) =


9.43064E-02	0.82267	0.40266
0.26413	0.32497	0.9931

Now swap dimension 2 with dimension 3.

CALL SWAP(a3, b3, 1,3,2)
CALL Display(MdEncode(a3), "a3=")

a3=( :, :, 1 ) =


0.85128	9.43064E-02
0.61923	0.26413

( :, :, 2 ) =


7.97914E-03	0.82267
2.30844E-02	0.32497

( :, :, 3 ) =


0.12877	0.40266
0.67707	0.9931

You can verify that the dimension 2 and dimension 3 are changed.

END PROGRAM main

Interface 3

܀ Interface
️܀ See example
↢

INTERFACE
  MODULE PURE SUBROUTINE Swap(a, b, i1, i2, i3, i4)
    REAL(Real64), ALLOCATABLE, INTENT(INOUT) :: a(:, :, :, :)
    !! the returned array
    REAL(Real64), INTENT(IN) :: b(:, :, :, :)
    !! input array, it will be untouched
    INTEGER(I4B), INTENT(IN) :: i1
    !! index 1 is Swapped with index `i1`
    !! make sure i1 is lesser than or equal to 4
    INTEGER(I4B), INTENT(IN) :: i2
    !! index 2 is Swapped with index `i2`
    !! make sure i2 is less than or equal to 4
    INTEGER(I4B), INTENT(IN) :: i3
    !! index 3 is Swapped with index `i3`
    !! make sure i3 is less than or equal to 4
    INTEGER(I4B), INTENT(IN) :: i4
    !! index 4 is Swapped with index `i4`
    !! make sure i4 is less than or equal to 4
  END SUBROUTINE Swap
END INTERFACE

This example shows the usage of Swap method.

Swap method for rank4.

PROGRAM main
    USE easifemBase
    IMPLICIT NONE
    REAL( DFP ), ALLOCATABLE :: a2(:,:), b2(:,:), a3(:,:,:), b3(:,:,:), &
      & a4(:,:,:,:), b4(:,:,:,:)

call reallocate(a2, 2,2)
call reallocate(b2, 2,2)
a2(1,:) = [2,1]
a2(2,:) = [4,2]
b2(1,1) = 1; b2(2,2) = 2
b4 = outerprod(a2, b2)
call swap(a=a4, b=b4, i1=1, i2=2, i3=3, i4=4)
call display(MdEncode(a4), "a4")

a4(:,:,1,1) =


2	1
4	2

(:,:,2,1) =


0	0
0	0

(:,:,1,2) =


0	0
0	0

(:,:,2,2) =


4	2
8	4

call swap(a=a4, b=b4, i1=1, i2=3, i3=2, i4=4)
call display(MdEncode(a4), "a4")

a4(:,:,1,1) =


2	0
4	0

(:,:,2,1) =


1	0
2	0

(:,:,1,2) =


0	4
0	8

(:,:,2,2) =


0	2
0	4

END PROGRAM main

Interface 4

܀ Interface
️܀ See example
↢

INTERFACE
  MODULE PURE SUBROUTINE Swap(a, b)
    INTEGER(Int8| Int16 | Int32 | Int64| Real32 | Real64), INTENT(INOUT) :: a, b
  END SUBROUTINE Swap
END INTERFACE

Swap two scalar numbers.

program main
use easifemBase
implicit none

real(dfp) :: a, b

a = 3; b=4
CALL Swap(a,b)
CALL OK(a.EQ.4 .AND. b.EQ.3, "test(1):")
end program main

Interface 5

܀ Interface
️܀ See example
↢

INTERFACE
  MODULE PURE SUBROUTINE Swap(a, b)
    INTEGER(Int8| Int16 | Int32 | Int64 | Real32 | Real64), INTENT(INOUT) :: a(:), b(:)
  END SUBROUTINE Swap
END INTERFACE

program main
use easifemBase
implicit none

real(dfp) :: a(3), b(3)

a = 3; b=4
CALL Swap(a,b)
CALL OK(ALL(a.EQ.4) .AND. ALL(b.EQ.3), "test(1):")
end program main

Interface 6

܀ Interface
️܀ See example
↢

INTERFACE
  MODULE PURE SUBROUTINE Swap(a, b)
    INTEGER(Int8| Int16 | Int32 | Int64 | Real32 | Real64), INTENT(INOUT) :: a(:,:), b(:,:)
  END SUBROUTINE Swap
END INTERFACE

program main
use easifemBase
implicit none

real(dfp) :: a(3, 2), b(3, 2)

a = 3; b=4
CALL Swap(a,b)
CALL OK(ALL(a.EQ.4) .AND. ALL(b.EQ.3), "test(1):")
end program main

Interface 7

܀ Interface
️܀ See example
↢

INTERFACE
  MODULE PURE SUBROUTINE Swap(a, b, mask)
    INTEGER(Int8| Int16 | Int32 | Int64 | Real32 | Real64), INTENT(INOUT) :: a, b
    LOGICAL(LGT), INTENT(IN) :: mask
  END SUBROUTINE Swap
END INTERFACE

Masked swap.

program main
use easifemBase
implicit none

real(dfp) :: a, b

a = 3; b=4
CALL Swap(a,b, a .LE.b )
CALL OK(a.EQ.4 .AND. b.EQ.3, "test(1):")


CALL Swap(a,b, a .LE.b )
CALL OK(a.EQ.4 .AND. b.EQ.3, "test(2):")
end program main

Interface 8

܀ Interface
️܀ See example
↢

INTERFACE
  MODULE PURE SUBROUTINE Swap(a, b, mask)
    INTEGER(Int8| Int16 | Int32 | Int64 | Real32 | Real64), INTENT(INOUT) :: a(:), b(:)
    LOGICAL(LGT), INTENT(IN) :: mask(:)
  END SUBROUTINE Swap
END INTERFACE

program main
use easifemBase
implicit none

real(dfp) :: a(2), b(2)

a = 3; b=4
CALL Swap(a,b, a .LE.b )
CALL OK(ALL(a.EQ.4 .AND. b.EQ.3), "test(1):")


CALL Swap(a,b, a .LE.b )
CALL OK(ALL(a.EQ.4 .AND. b.EQ.3), "test(2):")
end program main

Interface 9

܀ Interface
️܀ See example
↢

INTERFACE
  MODULE PURE SUBROUTINE Swap(a, b, mask)
    INTEGER(Int8| Int16 | Int32 | Int64 | Real32 | Real64), INTENT(INOUT) :: a(:, :), b(:, :)
    LOGICAL(LGT), INTENT(IN) :: mask(:, :)
  END SUBROUTINE Swap
END INTERFACE

program main
use easifemBase
implicit none

real(dfp) :: a(2,2), b(2,2)

a = 3; b=4
CALL Swap(a,b, a .LE.b )
CALL OK(ALL(a.EQ.4 .AND. b.EQ.3), "test(1):")


CALL Swap(a,b, a .LE.b )
CALL OK(ALL(a.EQ.4 .AND. b.EQ.3), "test(2):")
end program main

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