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Inter-particle distances

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 is 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:

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

If the input array is normal ('N'), the xyz coordinates are in the leading dimension: [n][3] in C and (3,n) in Fortran.

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

! check for LDA
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

! check for LDB
if (iand(transab,1) == 0 .and. LDB < 3) then
 info = QMCKL_INVALID_ARG_9
 return
endif

if (iand(transab,1) == 1 .and. LDB < n) then
 info = QMCKL_INVALID_ARG_9
 return
endif

if (iand(transab,2) == 0 .and. LDB < 3) then
 info = QMCKL_INVALID_ARG_9
 return
endif

if (iand(transab,2) == 2 .and. LDB < n) then
 info = QMCKL_INVALID_ARG_9
 return
endif

! check for LDC
if (LDC < m) then
 info = QMCKL_INVALID_ARG_11
 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 is more efficient when A and B are transposed.

Rescaled Distance

qmckl_distance_rescaled

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

\[ C_{ij} = \left( 1 - \exp{-\kappa C_{ij}}\right)/\kappa \]

If the input array is normal ('N'), the xyz coordinates are in the leading dimension: [n][3] in C and (3,n) in Fortran.

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
double rescale_factor_kappa in Factor for calculating rescaled distances

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_rescaled (
      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,
      const double  rescale_factor_kappa);

Source 

integer function qmckl_distance_rescaled_f(context, transa, transb, m, n, &
 A, LDA, B, LDB, C, LDC, rescale_factor_kappa) &
 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,*)
real*8     , intent(in)  :: rescale_factor_kappa

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

rescale_factor_kappa_inv = 1.0d0/rescale_factor_kappa;

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

! check for LDA
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

! check for LDB
if (iand(transab,1) == 0 .and. LDB < 3) then
 info = QMCKL_INVALID_ARG_9
 return
endif

if (iand(transab,1) == 1 .and. LDB < n) then
 info = QMCKL_INVALID_ARG_9
 return
endif

if (iand(transab,2) == 0 .and. LDB < 3) then
 info = QMCKL_INVALID_ARG_9
 return
endif

if (iand(transab,2) == 2 .and. LDB < n) then
 info = QMCKL_INVALID_ARG_9
 return
endif

! check for LDC
if (LDC < m) then
 info = QMCKL_INVALID_ARG_11
 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)
       dist = dsqrt(x*x + y*y + z*z)
       C(i,j) = (1.0d0 - dexp(-rescale_factor_kappa * dist)) * rescale_factor_kappa_inv
    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)
       dist = dsqrt(x*x + y*y + z*z)
       C(i,j) = (1.0d0 - dexp(-rescale_factor_kappa * dist)) * rescale_factor_kappa_inv
    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)
       dist = dsqrt(x*x + y*y + z*z)
       C(i,j) = (1.0d0 - dexp(-rescale_factor_kappa * dist)) * rescale_factor_kappa_inv
    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)
       dist = dsqrt(x*x + y*y + z*z)
       C(i,j) = (1.0d0 - dexp(-rescale_factor_kappa * dist)) * rescale_factor_kappa_inv
    end do
 end do

end select

end function qmckl_distance_rescaled_f

Performance

This function is more efficient when A and B are transposed.

Rescaled Distance Derivatives

qmckl_distance_rescaled_deriv_e

qmckl_distance_rescaled_deriv_e computes the matrix of the gradient and laplacian of the rescaled distance with respect to the electron coordinates. The derivative is a rank 3 tensor. The first dimension has a dimension of 4 of which the first three coordinates contains the gradient vector and the last index is the laplacian.

\[ C_{ij} = \left( 1 - \exp{-\kappa C_{ij}}\right)/\kappa \]

Here the gradient is defined as follows:

\[ \nabla (C_{ij}(\mathbf{r}_{ee})) = \left(\frac{\delta C_{ij}(\mathbf{r}_{ee})}{\delta x},\frac{\delta C_{ij}(\mathbf{r}_{ee})}{\delta y},\frac{\delta C_{ij}(\mathbf{r}_{ee})}{\delta z} \right) \] and the laplacian is defined as follows:

\[ \triangle (C_{ij}(r_{ee})) = \frac{\delta^2}{\delta x^2} + \frac{\delta^2}{\delta y^2} + \frac{\delta^2}{\delta z^2} \]

Using the above three formulae, the expression for the gradient and laplacian is as follows:

\[ \frac{\delta C_{ij}(\mathbf{r}_{ee})}{\delta x} = \frac{|(x_i - x_j)|}{r_{ij}} (1 - \kappa R_{ij}) \]

\[ \frac{\delta C_{ij}(\mathbf{r}_{ee})}{\delta y} = \frac{|(y_i - y_j)|}{r_{ij}} (1 - \kappa R_{ij}) \]

\[ \frac{\delta C_{ij}(\mathbf{r}_{ee})}{\delta z} = \frac{|(z_i - z_j)|}{r_{ij}} (1 - \kappa R_{ij}) \]

\[ \Delta(C_{ij}(r_{ee}) = \left[ \frac{2}{r_{ij}} - \kappa \right] (1-\kappa R_{ij}) \]

If the input array is normal ('N'), the xyz coordinates are in the leading dimension: [n][3] in C and (3,n) in Fortran.

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[4][n][ldc] out Array containing the $4 \times m \times n$ matrix $C$
int64_t ldc in Leading dimension of array C
double rescale_factor_kappa in Factor for calculating rescaled distances derivatives

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 $4 \times m \times n \times 8$ bytes

C header 

qmckl_exit_code qmckl_distance_rescaled_deriv_e (
      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,
      const double  rescale_factor_kappa);

Source 

integer function qmckl_distance_rescaled_deriv_e_f(context, transa, transb, m, n, &
 A, LDA, B, LDB, C, LDC, rescale_factor_kappa) &
 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(4,ldc,*)
real*8     , intent(in)  :: rescale_factor_kappa

integer*8 :: i,j
real*8    :: x, y, z, dist, dist_inv
real*8    :: rescale_factor_kappa_inv, rij
integer   :: transab

rescale_factor_kappa_inv = 1.0d0/rescale_factor_kappa;

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

! check for LDA
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

! check for LDB
if (iand(transab,1) == 0 .and. LDB < 3) then
 info = QMCKL_INVALID_ARG_9
 return
endif

if (iand(transab,1) == 1 .and. LDB < n) then
 info = QMCKL_INVALID_ARG_9
 return
endif

if (iand(transab,2) == 0 .and. LDB < 3) then
 info = QMCKL_INVALID_ARG_9
 return
endif

if (iand(transab,2) == 2 .and. LDB < n) then
 info = QMCKL_INVALID_ARG_9
 return
endif

! check for LDC
if (LDC < m) then
 info = QMCKL_INVALID_ARG_11
 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)
       dist = dsqrt(x*x + y*y + z*z)
       dist_inv = 1.0d0/dist
       rij = (1.0d0 - dexp(-rescale_factor_kappa * dist)) * rescale_factor_kappa_inv
       C(1,i,j) = x * dist_inv * ( 1.0d0 - rescale_factor_kappa_inv * rij)
       C(2,i,j) = y * dist_inv * ( 1.0d0 - rescale_factor_kappa_inv * rij)
       C(3,i,j) = z * dist_inv * ( 1.0d0 - rescale_factor_kappa_inv * rij)
       C(4,i,j) = (2.0d0 * dist_inv - rescale_factor_kappa_inv) * ( 1.0d0 - rescale_factor_kappa_inv * rij)
    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)
       dist = dsqrt(x*x + y*y + z*z)
       dist_inv = 1.0d0/dist
       rij = (1.0d0 - dexp(-rescale_factor_kappa * dist)) * rescale_factor_kappa_inv
       C(1,i,j) = x * dist_inv * ( 1.0d0 - rescale_factor_kappa_inv * rij)
       C(2,i,j) = y * dist_inv * ( 1.0d0 - rescale_factor_kappa_inv * rij)
       C(3,i,j) = z * dist_inv * ( 1.0d0 - rescale_factor_kappa_inv * rij)
       C(4,i,j) = (2.0d0 * dist_inv - rescale_factor_kappa_inv) * ( 1.0d0 - rescale_factor_kappa_inv * rij)
    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)
       dist = dsqrt(x*x + y*y + z*z)
       dist_inv = 1.0d0/dist
       rij = (1.0d0 - dexp(-rescale_factor_kappa * dist)) * rescale_factor_kappa_inv
       C(1,i,j) = x * dist_inv * ( 1.0d0 - rescale_factor_kappa_inv * rij)
       C(2,i,j) = y * dist_inv * ( 1.0d0 - rescale_factor_kappa_inv * rij)
       C(3,i,j) = z * dist_inv * ( 1.0d0 - rescale_factor_kappa_inv * rij)
       C(4,i,j) = (2.0d0 * dist_inv - rescale_factor_kappa_inv) * ( 1.0d0 - rescale_factor_kappa_inv * rij)
    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)
       dist = dsqrt(x*x + y*y + z*z)
       dist_inv = 1.0d0/dist
       rij = (1.0d0 - dexp(-rescale_factor_kappa * dist)) * rescale_factor_kappa_inv
       C(1,i,j) = x * dist_inv * ( 1.0d0 - rescale_factor_kappa_inv * rij)
       C(2,i,j) = y * dist_inv * ( 1.0d0 - rescale_factor_kappa_inv * rij)
       C(3,i,j) = z * dist_inv * ( 1.0d0 - rescale_factor_kappa_inv * rij)
       C(4,i,j) = (2.0d0 * dist_inv - rescale_factor_kappa_inv) * ( 1.0d0 - rescale_factor_kappa_inv * rij)
    end do
 end do

end select

end function qmckl_distance_rescaled_deriv_e_f

Performance

This function is more efficient when A and B are transposed.