DiagIndx

DiagIndx returns the indices of elements along a diagonal of a square or rectangle matrix. The indices are returned a two dimensional array of integers. This array has two columns. First column stands for the row index and second column stands for column index.

܀ Interface

Interface

INTERFACE
  MODULE PURE FUNCTION DiagIndx(m, n, diagNo) RESULT(ans)
    INTEGER(I4B), INTENT(IN) :: m
    !! number of rows in matrix
    INTEGER(I4B), INTENT(IN) :: n
    !! number of columns in a matrix
    INTEGER(I4B), INTENT(IN) :: diagNo
    !! diagonal number
    INTEGER(I4B), ALLOCATABLE :: ans(:, :)
    !! size of diagonal
  END FUNCTION DiagIndx
END INTERFACE

️܀ Example

In this example we show the usage of DiagIndx routine.

program main
  use easifemBase

  call Display( DiagIndx(4, 4, 0), "(4,4), main diagonal = " )
  call Display( DiagIndx(4, 4, 1), "(4,4), first superdiagonal = " )
  call Display( DiagIndx(4, 4, 2), "(4,4), second superdiagonal = " )

Results:

(4,4), main diagonal =
-----------------------
         1  1
         2  2
         3  3
         4  4

(4,4), first superdiagonal =
-----------------------------
            1  2
            2  3
            3  4

(4,4), second superdiagonal =
------------------------------
             1  3
             2  4

  call Display( DiagIndx(4, 4, -1), "(4,4), first subdiagonal = " )
  call Display( DiagIndx(4, 4, -2), "(4,4), second subdiagonal = " )

Results:

(4,4), first subdiagonal =
---------------------------
           2  1
           3  2
           4  3

(4,4), second subdiagonal =
----------------------------
            3  1
            4  2

note

Let us now test DiagIndx for RECTANGLE matrix.

  call Display( DiagIndx(4, 7, 0), "(4, 7), main diagonal = " )
  call Display( DiagIndx(4, 7, 1), "(4, 7), first superdiagonal = " )
  call Display( DiagIndx(4, 7, 2), "(4, 7), second superdiagonal = " )
  call Display( DiagIndx(4, 7, 3), "(4,7), third superdiagonal = " )
  call Display( DiagIndx(4, 7, 4), "(4,7), fourth superdiagonal = " )
  call Display( DiagIndx(4, 7, 5), "(4,7), fifth superdiagonal = " )
  call Display( DiagIndx(4, 7, 6), "(4,7), sixth superdiagonal = " )

Results:

results

(4, 7), main diagonal =
------------------------
          1  1
          2  2
          3  3
          4  4

(4, 7), first superdiagonal =
------------------------------
             1  2
             2  3
             3  4
             4  5

(4, 7), second superdiagonal =
-------------------------------
             1  3
             2  4
             3  5
             4  6

(4,7), third superdiagonal =
-----------------------------
            1  4
            2  5
            3  6
            4  7

(4,7), fourth superdiagonal =
------------------------------
             1  5
             2  6
             3  7

(4,7), fifth superdiagonal =
-----------------------------
            1  6
            2  7

(4,7), sixth superdiagonal =
-----------------------------
            1  7

(4,7) 1:3 subdiagonal

  call Display( DiagIndx(4, 7, -1), "(4,7), first subdiagonal = " )
  call Display( DiagIndx(4, 7, -2), "(4,7), second subdiagonal = " )
  call Display( DiagIndx(4, 7, -3), "(4,7), thrid subdiagonal = " )

results

(4,7), first subdiagonal =
---------------------------
           2  1
           3  2
           4  3
(4,7), second subdiagonal =
----------------------------
            3  1
            4  2
(4,7), thrid subdiagonal =
---------------------------
           4  1

end program

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