qmckl/org/qmckl_distance.org

Inter-particle distances

• Squared distance
  • qmckl_distance_sq
    • Requirements
    • C header
    • Source
    • Performance
• Distance
  • qmckl_distance
    • Requirements
    • C header
    • Source
    • Performance

Functions for the computation of distances between particles.

Squared distance

qmckl_distance_sq

qmckl_distance_sq computes the matrix of the squared distances between all pairs of points in two sets, one point within each set:

\[ C_{ij} = \sum_{k=1}^3 (A_{k,i}-B_{k,j})^2 \]

qmckl_context	context	in	Global state
char	transa	in	Array A is 'N': Normal, 'T': Transposed
char	transb	in	Array B is 'N': Normal, 'T': Transposed
int64_t	m	in	Number of points in the first set
int64_t	n	in	Number of points in the second set
double	A[][lda]	in	Array containing the $m \times 3$ matrix $A$
int64_t	lda	in	Leading dimension of array A
double	B[][ldb]	in	Array containing the $n \times 3$ matrix $B$
int64_t	ldb	in	Leading dimension of array B
double	C[n][ldc]	out	Array containing the $m \times n$ matrix $C$
int64_t	ldc	in	Leading dimension of array C

Requirements

• context is not QMCKL_NULL_CONTEXT
• m > 0
• n > 0
• lda >= 3 if transa == 'N'
• lda >= m if transa == 'T'
• ldb >= 3 if transb == 'N'
• ldb >= n if transb == 'T'
• ldc >= m
• A is allocated with at least $3 \times m \times 8$ bytes
• B is allocated with at least $3 \times n \times 8$ bytes
• C is allocated with at least $m \times n \times 8$ bytes

C header

qmckl_exit_code qmckl_distance_sq (
      const qmckl_context context,
      const char transa,
      const char transb,
      const int64_t m,
      const int64_t n,
      const double* A,
      const int64_t lda,
      const double* B,
      const int64_t ldb,
      double* const C,
      const int64_t ldc );

Source

integer function qmckl_distance_sq_f(context, transa, transb, m, n, &
 A, LDA, B, LDB, C, LDC) &
 result(info)
use qmckl
implicit none
integer(qmckl_context)  , intent(in)  :: context
character  , intent(in)  :: transa, transb
integer*8  , intent(in)  :: m, n
integer*8  , intent(in)  :: lda
real*8     , intent(in)  :: A(lda,*)
integer*8  , intent(in)  :: ldb
real*8     , intent(in)  :: B(ldb,*)
integer*8  , intent(in)  :: ldc
real*8     , intent(out) :: C(ldc,*)

integer*8 :: i,j
real*8    :: x, y, z
integer   :: transab

info = QMCKL_SUCCESS

if (context == QMCKL_NULL_CONTEXT) then
 info = QMCKL_INVALID_CONTEXT
 return
endif

if (m <= 0_8) then
 info = QMCKL_INVALID_ARG_4
 return
endif

if (n <= 0_8) then
 info = QMCKL_INVALID_ARG_5
 return
endif

if (transa == 'N' .or. transa == 'n') then
 transab = 0
else if (transa == 'T' .or. transa == 't') then
 transab = 1
else
 transab = -100
endif

if (transb == 'N' .or. transb == 'n') then
 continue
else if (transa == 'T' .or. transa == 't') then
 transab = transab + 2
else
 transab = -100
endif

if (transab < 0) then
 info = QMCKL_INVALID_ARG_1
 return
endif

if (iand(transab,1) == 0 .and. LDA < 3) then
 info = QMCKL_INVALID_ARG_7
 return
endif

if (iand(transab,1) == 1 .and. LDA < m) then
 info = QMCKL_INVALID_ARG_7
 return
endif

if (iand(transab,2) == 0 .and. LDA < 3) then
 info = QMCKL_INVALID_ARG_7
 return
endif

if (iand(transab,2) == 2 .and. LDA < m) then
 info = QMCKL_INVALID_ARG_7
 return
endif


select case (transab)

case(0)

 do j=1,n
    do i=1,m
       x = A(1,i) - B(1,j)
       y = A(2,i) - B(2,j)
       z = A(3,i) - B(3,j)
       C(i,j) = x*x + y*y + z*z
    end do
 end do

case(1)

 do j=1,n
    do i=1,m
       x = A(i,1) - B(1,j)
       y = A(i,2) - B(2,j)
       z = A(i,3) - B(3,j)
       C(i,j) = x*x + y*y + z*z
    end do
 end do

case(2)

 do j=1,n
    do i=1,m
       x = A(1,i) - B(j,1)
       y = A(2,i) - B(j,2)
       z = A(3,i) - B(j,3)
       C(i,j) = x*x + y*y + z*z
    end do
 end do

case(3)

 do j=1,n
    do i=1,m
       x = A(i,1) - B(j,1)
       y = A(i,2) - B(j,2)
       z = A(i,3) - B(j,3)
       C(i,j) = x*x + y*y + z*z
    end do
 end do

end select

end function qmckl_distance_sq_f

Performance

This function might be more efficient when A and B are transposed.

Distance

qmckl_distance

qmckl_distance computes the matrix of the distances between all pairs of points in two sets, one point within each set:

\[ C_{ij} = \sqrt{\sum_{k=1}^3 (A_{k,i}-B_{k,j})^2} \]

qmckl_context	context	in	Global state
char	transa	in	Array A is 'N': Normal, 'T': Transposed
char	transb	in	Array B is 'N': Normal, 'T': Transposed
int64_t	m	in	Number of points in the first set
int64_t	n	in	Number of points in the second set
double	A[][lda]	in	Array containing the $m \times 3$ matrix $A$
int64_t	lda	in	Leading dimension of array A
double	B[][ldb]	in	Array containing the $n \times 3$ matrix $B$
int64_t	ldb	in	Leading dimension of array B
double	C[n][ldc]	out	Array containing the $m \times n$ matrix $C$
int64_t	ldc	in	Leading dimension of array C

Requirements

• context is not QMCKL_NULL_CONTEXT
• m > 0
• n > 0
• lda >= 3 if transa == 'N'
• lda >= m if transa == 'T'
• ldb >= 3 if transb == 'N'
• ldb >= n if transb == 'T'
• ldc >= m
• A is allocated with at least $3 \times m \times 8$ bytes
• B is allocated with at least $3 \times n \times 8$ bytes
• C is allocated with at least $m \times n \times 8$ bytes

C header

qmckl_exit_code qmckl_distance (
      const qmckl_context context,
      const char transa,
      const char transb,
      const int64_t m,
      const int64_t n,
      const double* A,
      const int64_t lda,
      const double* B,
      const int64_t ldb,
      double* const C,
      const int64_t ldc );

Source

integer function qmckl_distance_f(context, transa, transb, m, n, &
 A, LDA, B, LDB, C, LDC) &
 result(info)
use qmckl
implicit none
integer(qmckl_context)  , intent(in)  :: context
character  , intent(in)  :: transa, transb
integer*8  , intent(in)  :: m, n
integer*8  , intent(in)  :: lda
real*8     , intent(in)  :: A(lda,*)
integer*8  , intent(in)  :: ldb
real*8     , intent(in)  :: B(ldb,*)
integer*8  , intent(in)  :: ldc
real*8     , intent(out) :: C(ldc,*)

integer*8 :: i,j
real*8    :: x, y, z
integer   :: transab

info = QMCKL_SUCCESS

if (context == QMCKL_NULL_CONTEXT) then
 info = QMCKL_INVALID_CONTEXT
 return
endif

if (m <= 0_8) then
 info = QMCKL_INVALID_ARG_4
 return
endif

if (n <= 0_8) then
 info = QMCKL_INVALID_ARG_5
 return
endif

if (transa == 'N' .or. transa == 'n') then
 transab = 0
else if (transa == 'T' .or. transa == 't') then
 transab = 1
else
 transab = -100
endif

if (transb == 'N' .or. transb == 'n') then
 continue
else if (transa == 'T' .or. transa == 't') then
 transab = transab + 2
else
 transab = -100
endif

if (transab < 0) then
 info = QMCKL_INVALID_ARG_1
 return
endif

if (iand(transab,1) == 0 .and. LDA < 3) then
 info = QMCKL_INVALID_ARG_7
 return
endif

if (iand(transab,1) == 1 .and. LDA < m) then
 info = QMCKL_INVALID_ARG_7
 return
endif

if (iand(transab,2) == 0 .and. LDA < 3) then
 info = QMCKL_INVALID_ARG_7
 return
endif

if (iand(transab,2) == 2 .and. LDA < m) then
 info = QMCKL_INVALID_ARG_7
 return
endif


select case (transab)

case(0)

 do j=1,n
    do i=1,m
       x = A(1,i) - B(1,j)
       y = A(2,i) - B(2,j)
       z = A(3,i) - B(3,j)
       C(i,j) = x*x + y*y + z*z
    end do
    C(:,j) = dsqrt(C(:,j))
 end do

case(1)

 do j=1,n
    do i=1,m
       x = A(i,1) - B(1,j)
       y = A(i,2) - B(2,j)
       z = A(i,3) - B(3,j)
       C(i,j) = x*x + y*y + z*z
    end do
    C(:,j) = dsqrt(C(:,j))
 end do

case(2)

 do j=1,n
    do i=1,m
       x = A(1,i) - B(j,1)
       y = A(2,i) - B(j,2)
       z = A(3,i) - B(j,3)
       C(i,j) = x*x + y*y + z*z
    end do
    C(:,j) = dsqrt(C(:,j))
 end do

case(3)

 do j=1,n
    do i=1,m
       x = A(i,1) - B(j,1)
       y = A(i,2) - B(j,2)
       z = A(i,3) - B(j,3)
       C(i,j) = x*x + y*y + z*z
    end do
    C(:,j) = dsqrt(C(:,j))
 end do

end select

end function qmckl_distance_f

Performance

This function might be more efficient when A and B are transposed.