Adding option to doc files, clarifying normal forces in compute pair/bond local

doc/src/bond_bpm_rotational.rst

@@ -30,6 +30,9 @@ Syntax
        *smooth* value = *yes* or *no*
           smooths bond forces near the breaking point
 
+       *normalize* value = *yes* or *no*
+          normalizes normal and shear forces by the reference length
+
        *break/no*
           indicates that bonds should not break during a run
 
@@ -136,6 +139,9 @@ or :doc:`read_restart <read_restart>` commands:
 * :math:`\gamma_r`      (force*distance/velocity units)
 * :math:`\gamma_t`      (force*distance/velocity units)
 
+However, the *normalize* option will normalize the radial and shear forces
+by :math:`r_0` such that :math:`k_r` and :math:`k_s` are unit less.
+
 By default, pair forces are not calculated between bonded particles.
 Pair forces can alternatively be overlaid on top of bond forces using
 the *overlay/pair* keyword. These settings require specific

doc/src/bond_bpm_spring.rst

@@ -30,6 +30,9 @@ Syntax
        *smooth* value = *yes* or *no*
           smooths bond forces near the breaking point
 
+       *normalize* value = *yes* or *no*
+          normalizes bond forces by their reference length
+
        *break/no*
           indicates that bonds should not break during a run
 
@@ -66,7 +69,7 @@ particles based on a model described by Clemmer and Robbins
 
    F = k (r - r_0) w
 
-where :math:`k_r` is a stiffness, :math:`r` is the current distance
+where :math:`k` is a stiffness, :math:`r` is the current distance
 and :math:`r_0` is the initial distance between the two particles, and
 :math:`w` is an optional smoothing factor discussed below. Bonds will
 break at a strain of :math:`\epsilon_c`.  This is done by setting by
@@ -102,6 +105,9 @@ the data file or restart files read by the :doc:`read_data
 * :math:`\epsilon_c`    (unit less)
 * :math:`\gamma`        (force/velocity units)
 
+However, the *normalize* option will normalize the elastic bond force by
+:math:`r_0` such that :math:`k` is unit less.
+
 By default, pair forces are not calculated between bonded particles.
 Pair forces can alternatively be overlaid on top of bond forces using
 the *overlay/pair* keyword. These settings require specific

doc/src/compute_bond_local.rst

@@ -76,7 +76,10 @@ The value *force* is the magnitude of the force acting between the
 pair of atoms in the bond.
 
 The values *fx*, *fy*, and *fz* are the xyz components of
-*force* between the pair of atoms in the bond.
+*force* between the pair of atoms in the bond. For bond styles that apply
+non-central forces, such as :doc:`bond_style bpm/rotational
+<bond_bpm_rotational>`, these values only include the :math:`(x,y,z)`
+components of the normal force component.
 
 The remaining properties are all computed for motion of the two atoms
 relative to the center of mass (COM) velocity of the 2 atoms in the

doc/src/compute_pair_local.rst

@@ -66,7 +66,9 @@ The value *eng* is the interaction energy for the pair of atoms.
 The value *force* is the force acting between the pair of atoms, which
 is positive for a repulsive force and negative for an attractive
 force.  The values *fx*, *fy*, and *fz* are the :math:`(x,y,z)` components of
-*force* on atom I.
+*force* on atom I. For pair styles that apply non-central forces,
+such as :doc:`granular pair styles <pair_gran>`, these values only include
+the :math:`(x,y,z)` components of the normal force component.
 
 A pair style may define additional pairwise quantities which can be
 accessed as *p1* to *pN*, where :math:`N` is defined by the pair style.