+
+/*! \brief spread force to 4 centers
+ *
+ * \tparam T The type of vector, e.g. float, double, etc
+ * \param dxIJ Distance between centers i and j
+ * \param dxKJ Distance between centers j and k
+ * \param dxKL Distance between centers k and l
+ * \param m Cross product of \p dxIJ x \p dxKJ
+ * \param m Cross product of \p dxKJ x \p dxKL
+ * \param force_i Force on center i
+ * \param force_j Force on center j
+ * \param force_k Force on center k
+ * \param force_k Force on center l
+ * \param shf_ik Shift force between centers i and j
+ * \param shf_kj Shift force between centers k and j
+ * \param shf_lj Shift force between centers k and j
+ * \param shf_c Shift force at the center subtending the angle
+ */