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Tril

This function returns the lower triangle part of a matrix.

Interface 1​

  MODULE PURE FUNCTION Tril(A, diagNo) RESULT(ans)
    INTEGER(Int8| Int16 | Int32 | Int64) | REAL(Real32| Real64), INTENT(IN) :: A(:, :)
    INTEGER(I4B), OPTIONAL, INTENT(IN) :: diagNo
    !! diagonal number, default = 0
    INTEGER(Int8| Int16 | Int32 | Int64) | REAL(Real32| Real64) :: ans(SIZE(A, 1), SIZE(A, 2))
  END FUNCTION Tril

Interface 2​

MODULE PURE FUNCTION Tril_12(A, flate, diagNo) RESULT(ans)
  INTEGER(Int8| Int16 | Int32 | Int64) | REAL(Real32| Real64), INTENT(IN) :: A(:, :)
  LOGICAL(LGT), INTENT(IN) :: flate
  !! This variable is only for creating unique interface
  INTEGER(I4B), OPTIONAL, INTENT(IN) :: diagNo
  !! diagonal number, default = 0
  INTEGER(Int8| Int16 | Int32 | Int64) | REAL(Real32| Real64), ALLOCATABLE :: ans(:)
END FUNCTION Tril_12

In this case the lower triangular part is returned in flat form. That is, the first n entries of ans denotes the main diagonal. Then next n-1 entries denotes first subdiagonal, and so on.