Add support for nonzero ds to app input.

Author: cemitch99

docs/source/usage/parameters.rst

@@ -363,6 +363,7 @@ Lattice Elements
 
             * ``<element_name>.R(i,j)`` (``float``, ...) matrix entries
                 a 1-indexed, 6x6, linear transport map to multiply with the the phase space vector :math:`x,px,y,py,t,pt`.
+            * ``<element_name>.ds`` (``float``, in meters) length associated with a user-defined linear element (defaults to 0)
             * ``<element_name>.dx`` (``float``, in meters) horizontal translation error
             * ``<element_name>.dy`` (``float``, in meters) vertical translation error
             * ``<element_name>.rotation`` (``float``, in degrees) rotation error in the transverse plane

docs/source/usage/python.rst

@@ -624,6 +624,7 @@ This module provides elements for the accelerator lattice.
    up to the user to ensure that the matrix :math:`R` is symplectic.  Otherwise, this condition may be violated.
 
    :param R: a linear transport map to multiply with the the phase space vector :math:`(x,px,y,py,t,pt)`.
+   :param ds: length associated with a user-defined linear element (defaults to 0), in m
    :param dx: horizontal translation error in m
    :param dy: vertical translation error in m
    :param rotation: rotation error in the transverse plane [degrees]

examples/fodo_userdef/input_fodo_userdef.in

@@ -28,6 +28,7 @@ monitor.type = beam_monitor
 monitor.backend = h5
 
 drift1.type = linear_map
+drift1.ds = 0.25
 drift1.R12 = 0.25            # ds
 drift1.R34 = 0.25            # ds
 drift1.R56 = 0.25 / 16.6464  # ds / (beta*gamma^2)
@@ -37,6 +38,7 @@ quad1.ds = 1.0
 quad1.k = 1.0
 
 drift2.type = linear_map
+drift2.ds = 0.5
 drift2.R12 = 0.5            # ds
 drift2.R34 = 0.5            # ds
 drift2.R56 = 0.5 / 16.6464  # ds / (beta*gamma^2)

src/initialization/InitElement.cpp

@@ -462,6 +462,9 @@ namespace detail
         {
             auto a = detail::query_alignment(pp_element);
 
+            amrex::ParticleReal ds = 0.0;
+            pp_element.queryAdd("ds", ds);
+
             elements::LinearTransport::Map6x6 transport_map = elements::LinearTransport::Map6x6::Identity();
 
             // safe to ParmParse inputs for reproducibility
@@ -472,7 +475,7 @@ namespace detail
                 }
             }
 
-            m_lattice.emplace_back(LinearMap(transport_map, a["dx"], a["dy"], a["rotation_degree"]) );
+            m_lattice.emplace_back(LinearMap(transport_map, ds, a["dx"], a["dy"], a["rotation_degree"]) );
         } else {
             amrex::Abort("Unknown type for lattice element " + element_name + ": " + element_type);
         }