Honor the value of forceNoPBC when comparing values of distanceVec va…

…riables
Colvars · Dec 4, 2023 · e75f004 · e75f004
1 parent 6e02473
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diff --git a/doc/colvars-refman-main.tex b/doc/colvars-refman-main.tex
@@ -1651,11 +1651,11 @@
 \cvsubsubsec{\texttt{distanceVec}: distance vector  between two groups.}{sec:cvc_distanceVec}
 \labelkey{colvar|distanceVec}
 
-The \texttt{distanceVec~\{...\}} block defines
-a distance vector component, which accepts the same keywords as
-the component \texttt{distance}: \texttt{group1}, \texttt{group2}, and
-\texttt{forceNoPBC}. Its value is the 3-vector joining the centers
-of mass of \texttt{group1} and \texttt{group2}.
+The \texttt{distanceVec} component computes the 3-dimensional vector joining the centers of mass of
+\texttt{group1} and \texttt{group2}.  Its values are therefore multi-dimensional and are subject to
+the restrictions listed in \ref{sec:cvc_non_scalar}.  Moreover, when computing differences between
+two different values of a \texttt{distanceVec} variable the minimum-image convention is assumed
+(unless \refkey{forceNoPBC}{colvar|cvc|forceNoPBC} is enabled).
 
 \begin{cvcoptions}
 \item %

diff --git a/src/colvarcomp_distances.cpp b/src/colvarcomp_distances.cpp
@@ -125,27 +125,32 @@ void colvar::distance_vec::apply_force(colvarvalue const &force)
 }
 
 
-cvm::real colvar::distance_vec::dist2(colvarvalue const &x1,
-                                      colvarvalue const &x2) const
+cvm::real colvar::distance_vec::dist2(colvarvalue const &x1, colvarvalue const &x2) const
 {
-  return (cvm::position_distance(x1.rvector_value, x2.rvector_value)).norm2();
+  if (is_enabled(f_cvc_pbc_minimum_image)) {
+    return (cvm::position_distance(x1.rvector_value, x2.rvector_value)).norm2();
+  }
+  return (x2.rvector_value - x1.rvector_value).norm2();
 }
 
 
-colvarvalue colvar::distance_vec::dist2_lgrad(colvarvalue const &x1,
-                                              colvarvalue const &x2) const
+colvarvalue colvar::distance_vec::dist2_lgrad(colvarvalue const &x1, colvarvalue const &x2) const
 {
-  return 2.0 * cvm::position_distance(x2.rvector_value, x1.rvector_value);
+  if (is_enabled(f_cvc_pbc_minimum_image)) {
+    return cvm::position_distance(x1.rvector_value, x2.rvector_value);
+  }
+  return 2.0 * (x2.rvector_value - x1.rvector_value);
 }
 
 
-colvarvalue colvar::distance_vec::dist2_rgrad(colvarvalue const &x1,
-                                              colvarvalue const &x2) const
+colvarvalue colvar::distance_vec::dist2_rgrad(colvarvalue const &x1, colvarvalue const &x2) const
 {
-  return 2.0 * cvm::position_distance(x2.rvector_value, x1.rvector_value);
+  return distance_vec::dist2_lgrad(x1, x2);
 }
 
 
+void colvar::distance_vec::wrap(colvarvalue & /* x_unwrapped */) const {}
+
 
 colvar::distance_z::distance_z()
 {