2020-10-22 00:50:07 +02:00
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# -*- mode: org -*-
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# vim: syntax=c
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#+TITLE: Computation of distances
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2020-10-22 01:24:14 +02:00
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2020-10-22 00:50:07 +02:00
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Function for the computation of distances between particles.
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3 files are produced:
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2020-10-22 01:24:14 +02:00
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- a header file : =qmckl_distance.h=
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- a source file : =qmckl_distance.f90=
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- a test file : =test_qmckl_distance.c=
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2020-10-22 00:50:07 +02:00
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2020-10-22 01:24:14 +02:00
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*** Header
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2020-10-22 00:50:07 +02:00
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#+BEGIN_SRC C :comments link :tangle qmckl_distance.h
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#ifndef QMCKL_DISTANCE_H
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#define QMCKL_DISTANCE_H
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#include "qmckl_context.h"
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#+END_SRC
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*** Source
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#+BEGIN_SRC f90 :comments link :tangle qmckl_distance.f90
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#+END_SRC
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*** Test
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#+BEGIN_SRC C :comments link :tangle test_qmckl_distance.c
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#include <math.h>
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#include "qmckl.h"
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#include "munit.h"
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MunitResult test_qmckl_distance() {
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qmckl_context context;
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int64_t m, n, LDA, LDB, LDC;
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double *A, *B, *C ;
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int i, j;
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context = qmckl_context_create();
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m = 5;
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2020-10-22 01:24:14 +02:00
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n = 6;
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2020-10-22 00:50:07 +02:00
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LDA = 6;
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LDB = 10;
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LDC = 5;
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A = (double*) qmckl_malloc (context, LDA*4*sizeof(double));
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B = (double*) qmckl_malloc (context, LDB*3*sizeof(double));
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C = (double*) qmckl_malloc (context, LDC*n*sizeof(double));
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for (j=0 ; j<3 ; j++) {
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for (i=0 ; i<m ; i++) {
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A[i+j*LDA] = -10. + (double) (i+j);
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}
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}
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for (j=0 ; j<3 ; j++) {
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for (i=0 ; i<n ; i++) {
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B[i+j*LDB] = -1. + (double) (i*j);
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}
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}
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#+END_SRC
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* Squared distance
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** =qmckl_distance_sq=
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2020-10-22 01:24:14 +02:00
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2020-10-22 00:50:07 +02:00
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Computes the matrix of the squared distances between all pairs of
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points in two sets, one point within each set:
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\[
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C_{ij} = \sum_{k=1}^3 (A_{i,k}-B_{j,k})^2
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\]
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2020-10-22 00:50:07 +02:00
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*** Arguments
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| =context= | input | Global state |
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| =m= | input | Number of points in the first set |
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| =n= | input | Number of points in the second set |
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| =LDA= | input | Leading dimension of array =A= |
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| =A= | input | Array containing the $3 \times m$ matrix $A$ |
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| =LDB= | input | Leading dimension of array =B= |
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| =B= | input | Array containing the $3 \times n$ matrix $B$ |
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| =LDC= | input | Leading dimension of array =C= |
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| =C= | output | Array containing the $m \times n$ matrix $C$ |
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| =info= | output | exit status is zero upon success |
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*** Requirements
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- =context= is not 0
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- =m= > 0
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- =n= > 0
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- =LDA= >= m
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- =LDB= >= n
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- =LDC= >= m
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- =A= is allocated with at least $3 \times m \times 8$ bytes
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- =B= is allocated with at least $3 \times n \times 8$ bytes
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- =C= is allocated with at least $m \times n \times 8$ bytes
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*** Header
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#+BEGIN_SRC C :comments link :tangle qmckl_distance.h
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2020-10-22 01:24:14 +02:00
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qmckl_exit_code qmckl_distance_sq(qmckl_context context,
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int64_t m, int64_t n,
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double *A, int64_t LDA,
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double *B, int64_t LDB,
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double *C, int64_t LDC);
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#+END_SRC
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*** Source
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#+BEGIN_SRC f90 :comments link :tangle qmckl_distance.f90
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integer(c_int32_t) function qmckl_distance_sq(context, m, n, A, LDA, B, LDB, C, LDC) &
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bind(C) result(info)
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use, intrinsic :: iso_c_binding
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implicit none
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integer (c_int64_t) , intent(in) , value :: context
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integer (c_int64_t) , intent(in) , value :: m, n
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integer (c_int64_t) , intent(in) , value :: LDA
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real (c_double) , intent(in) :: A(LDA,3)
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integer (c_int64_t) , intent(in) , value :: LDB
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real (c_double) , intent(in) :: B(LDB,3)
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integer (c_int64_t) , intent(in) , value :: LDC
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real (c_double) , intent(out) :: C(LDC,n)
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2020-10-22 00:50:07 +02:00
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integer (c_int64_t) :: i,j
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real (c_double) :: x, y, z
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2020-10-22 00:50:07 +02:00
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info = 0
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2020-10-22 00:50:07 +02:00
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if (context == 0_8) then
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info = -1
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return
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endif
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2020-10-22 00:50:07 +02:00
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if (m <= 0_8) then
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info = -2
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return
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endif
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2020-10-22 00:50:07 +02:00
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if (n <= 0_8) then
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info = -3
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return
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endif
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2020-10-22 00:50:07 +02:00
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if (LDA < m) then
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info = -4
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return
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endif
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2020-10-22 00:50:07 +02:00
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if (LDB < n) then
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info = -5
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return
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endif
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2020-10-22 00:50:07 +02:00
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if (LDC < m) then
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info = -6
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return
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endif
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2020-10-22 01:24:14 +02:00
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2020-10-22 00:50:07 +02:00
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do j=1,n
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do i=1,m
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x = A(i,1) - B(j,1)
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y = A(i,2) - B(j,2)
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z = A(i,3) - B(j,3)
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C(i,j) = x*x + y*y + z*z
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end do
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end do
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2020-10-22 00:50:07 +02:00
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end function qmckl_distance_sq
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#+END_SRC
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*** Test
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#+BEGIN_SRC C :comments link :tangle test_qmckl_distance.c
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2020-10-22 01:24:14 +02:00
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munit_assert_int64(QMCKL_SUCCESS, ==,
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qmckl_distance_sq(context, m, n, A, LDA, B, LDB, C, LDC) );
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for (j=0 ; j<n ; j++) {
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for (i=0 ; i<m ; i++) {
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munit_assert_double_equal(C[i+j*LDC],
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pow(A[i ]-B[j ],2) +
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pow(A[i+ LDA]-B[j+ LDB],2) +
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pow(A[i+2*LDA]-B[j+2*LDB],2) ,
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14 );
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}
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2020-10-22 01:24:14 +02:00
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}
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2020-10-22 00:50:07 +02:00
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#+END_SRC
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* End of files
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*** Header
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#+BEGIN_SRC C :comments link :tangle qmckl_distance.h
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#endif
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#+END_SRC
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*** Test
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#+BEGIN_SRC C :comments link :tangle test_qmckl_distance.c
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qmckl_free(A);
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qmckl_free(B);
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qmckl_free(C);
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if (qmckl_context_destroy(context) != QMCKL_SUCCESS)
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return QMCKL_FAILURE;
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return MUNIT_OK;
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}
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#+END_SRC
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