pic_dgemm Subroutine

   pure subroutine pic_dgemm(A, B, C, transa, transb, alpha, beta)
      !! interface for single precision matrix multiplication
      real(dp), intent(in) :: A(:, :)
      real(dp), intent(in) :: B(:, :)
      real(dp), intent(inout) :: C(:, :)
      character(len=1), intent(in), optional :: transa
      character(len=1), intent(in), optional :: transb
      real(dp), intent(in), optional :: alpha
      real(dp), intent(in), optional :: beta
      character(len=1) :: OP_A, OP_B
      real(dp) :: l_alpha, l_beta
      integer(default_int) :: m, n, k, lda, ldb, ldc

      ! first check for the constants
      if (present(alpha)) then
         l_alpha = alpha
      else
         l_alpha = 1.0_sp
      end if
      if (present(beta)) then
         l_beta = beta
      else
         l_beta = 0.0_sp
      end if
      ! check the OP options, maybe this should not be optional
      if (present(transa)) then
         OP_A = transa
      else
         OP_A = "N"
      end if
      if (present(transb)) then
         OP_B = transb
      else
         OP_B = "N"
      end if

      ! check for the dimensions now
      if ((OP_A == "N" .or. OP_A == "n")) then
         k = size(A, 2)
      else
         k = size(A, 1)
      end if

      ! get LDA, LDB, and LDC
      lda = max(1, size(A, 1))
      ldb = max(1, size(B, 1))
      ldc = max(1, size(C, 1))
      m = size(C, 1)
      n = size(C, 2)

      call blas_gemm(OP_A, OP_B, m, n, k, l_alpha, A, lda, B, ldb, l_beta, C, ldc)

   end subroutine pic_dgemm