stdlib_ssyr2k Subroutine

     pure subroutine stdlib_ssyr2k(uplo,trans,n,k,alpha,a,lda,b,ldb,beta,c,ldc)
     !! SSYR2K performs one of the symmetric rank 2k operations
     !! C := alpha*A*B**T + alpha*B*A**T + beta*C,
     !! or
     !! C := alpha*A**T*B + alpha*B**T*A + beta*C,
     !! where  alpha and beta  are scalars, C is an  n by n  symmetric matrix
     !! and  A and B  are  n by k  matrices  in the  first  case  and  k by n
     !! matrices in the second case.
        ! -- reference blas level3 routine --
        ! -- reference blas is a software package provided by univ. of tennessee,    --
        ! -- univ. of california berkeley, univ. of colorado denver and nag ltd..--
           ! Scalar Arguments 
           real(sp), intent(in) :: alpha, beta
           integer(ilp), intent(in) :: k, lda, ldb, ldc, n
           character, intent(in) :: trans, uplo
           ! Array Arguments 
           real(sp), intent(in) :: a(lda,*), b(ldb,*)
           real(sp), intent(inout) :: c(ldc,*)
        ! =====================================================================
           ! Intrinsic Functions 
           intrinsic :: max
           ! Local Scalars 
           real(sp) :: temp1, temp2
           integer(ilp) :: i, info, j, l, nrowa
           logical(lk) :: upper
           
           ! test the input parameters.
           if (stdlib_lsame(trans,'N')) then
               nrowa = n
           else
               nrowa = k
           end if
           upper = stdlib_lsame(uplo,'U')
           info = 0
           if ((.not.upper) .and. (.not.stdlib_lsame(uplo,'L'))) then
               info = 1
           else if ((.not.stdlib_lsame(trans,'N')) .and.(.not.stdlib_lsame(trans,'T')) .and.(&
                     .not.stdlib_lsame(trans,'C'))) then
               info = 2
           else if (n<0) then
               info = 3
           else if (k<0) then
               info = 4
           else if (lda<max(1,nrowa)) then
               info = 7
           else if (ldb<max(1,nrowa)) then
               info = 9
           else if (ldc<max(1,n)) then
               info = 12
           end if
           if (info/=0) then
               call stdlib_xerbla('SSYR2K',info)
               return
           end if
           ! quick return if possible.
           if ((n==0) .or. (((alpha==zero).or.(k==0)).and. (beta==one))) return
           ! and when  alpha.eq.zero.
           if (alpha==zero) then
               if (upper) then
                   if (beta==zero) then
                       do j = 1,n
                           do i = 1,j
                               c(i,j) = zero
                           end do
                       end do
                   else
                       do j = 1,n
                           do i = 1,j
                               c(i,j) = beta*c(i,j)
                           end do
                       end do
                   end if
               else
                   if (beta==zero) then
                       do j = 1,n
                           do i = j,n
                               c(i,j) = zero
                           end do
                       end do
                   else
                       do j = 1,n
                           do i = j,n
                               c(i,j) = beta*c(i,j)
                           end do
                       end do
                   end if
               end if
               return
           end if
           ! start the operations.
           if (stdlib_lsame(trans,'N')) then
              ! form  c := alpha*a*b**t + alpha*b*a**t + c.
               if (upper) then
                   do j = 1,n
                       if (beta==zero) then
                           do i = 1,j
                               c(i,j) = zero
                           end do
                       else if (beta/=one) then
                           do i = 1,j
                               c(i,j) = beta*c(i,j)
                           end do
                       end if
                       do l = 1,k
                           if ((a(j,l)/=zero) .or. (b(j,l)/=zero)) then
                               temp1 = alpha*b(j,l)
                               temp2 = alpha*a(j,l)
                               do i = 1,j
                                   c(i,j) = c(i,j) + a(i,l)*temp1 +b(i,l)*temp2
                               end do
                           end if
                       end do
                   end do
               else
                   do j = 1,n
                       if (beta==zero) then
                           do i = j,n
                               c(i,j) = zero
                           end do
                       else if (beta/=one) then
                           do i = j,n
                               c(i,j) = beta*c(i,j)
                           end do
                       end if
                       do l = 1,k
                           if ((a(j,l)/=zero) .or. (b(j,l)/=zero)) then
                               temp1 = alpha*b(j,l)
                               temp2 = alpha*a(j,l)
                               do i = j,n
                                   c(i,j) = c(i,j) + a(i,l)*temp1 +b(i,l)*temp2
                               end do
                           end if
                       end do
                   end do
               end if
           else
              ! form  c := alpha*a**t*b + alpha*b**t*a + c.
               if (upper) then
                   do j = 1,n
                       do i = 1,j
                           temp1 = zero
                           temp2 = zero
                           do l = 1,k
                               temp1 = temp1 + a(l,i)*b(l,j)
                               temp2 = temp2 + b(l,i)*a(l,j)
                           end do
                           if (beta==zero) then
                               c(i,j) = alpha*temp1 + alpha*temp2
                           else
                               c(i,j) = beta*c(i,j) + alpha*temp1 +alpha*temp2
                           end if
                       end do
                   end do
               else
                   do j = 1,n
                       do i = j,n
                           temp1 = zero
                           temp2 = zero
                           do l = 1,k
                               temp1 = temp1 + a(l,i)*b(l,j)
                               temp2 = temp2 + b(l,i)*a(l,j)
                           end do
                           if (beta==zero) then
                               c(i,j) = alpha*temp1 + alpha*temp2
                           else
                               c(i,j) = beta*c(i,j) + alpha*temp1 +alpha*temp2
                           end if
                       end do
                   end do
               end if
           end if
           return
     end subroutine stdlib_ssyr2k