Remove additional string for Twiss input (#698)

Improve maintainability by removing additional string "from_cs" that allows
for beam initialization from Twiss parameters.

docs/source/usage/parameters.rst

@@ -43,8 +43,8 @@ Initial Beam Distributions
         * ``beam.muypy`` (``float``, dimensionless, default: ``0``) correlation Y-Py
         * ``beam.mutpt`` (``float``, dimensionless, default: ``0``) correlation T-Pt
 
-    * Courant-Snyder / Twiss parameters.
-      To enable input via CS / Twiss parameters, add the suffix ``_from_cs`` or ``from_twiss`` to the name of the distribution.
+    * Courant-Snyder (Twiss) parameters.
+      To enable input via Courant-Snyder (Twiss) parameters, add the suffix ``from_twiss`` to the name of the distribution.
       Use the following parameters to characterize it:
 
         * ``beam.alphaX`` (``float``, dimensionless, default: ``0``) CS / Twiss :math:`\alpha` for X
@@ -59,21 +59,21 @@ Initial Beam Distributions
 
     The following distributions are available:
 
-    * ``waterbag`` or ``waterbag_from_cs``/``waterbag_from_twiss`` for initial Waterbag distribution.
+    * ``waterbag`` or ``waterbag_from_twiss`` for initial Waterbag distribution.
 
-    * ``kurth6d`` or ``kurth6d_from_cs``/``kurth6d_from_twiss`` for initial 6D Kurth distribution.
+    * ``kurth6d`` or ``kurth6d_from_twiss`` for initial 6D Kurth distribution.
 
-    * ``gaussian`` or ``gaussian_from_cs``/``gaussian_from_twiss`` for initial 6D Gaussian (normal) distribution.
+    * ``gaussian`` or ``gaussian_from_twiss`` for initial 6D Gaussian (normal) distribution.
 
-    * ``kvdist`` or ``kvdist_from_cs``/``kvdist_from_twiss`` for initial K-V distribution in the transverse plane.
+    * ``kvdist`` or ``kvdist_from_twiss`` for initial K-V distribution in the transverse plane.
       The distribution is uniform in t and Gaussian in pt.
 
-    * ``kurth4d`` or ``kurth4d_from_cs``/``kurth4d_from_twiss`` for initial 4D Kurth distribution in the transverse plane.
+    * ``kurth4d`` or ``kurth4d_from_twiss`` for initial 4D Kurth distribution in the transverse plane.
       The distribution is uniform in t and Gaussian in pt.
 
-    * ``semigaussian`` or ``semigaussian_from_cs``/``semigaussian_from_twiss`` for initial Semi-Gaussian distribution.  The distribution is uniform within a cylinder in (x,y,z) and Gaussian in momenta (px,py,pt).
+    * ``semigaussian`` or ``semigaussian_from_twiss`` for initial Semi-Gaussian distribution.  The distribution is uniform within a cylinder in (x,y,z) and Gaussian in momenta (px,py,pt).
 
-    * ``triangle`` or ``triangle_from_cs``/``triangle_from_twiss`` a triangle distribution for laser-plasma acceleration related applications.
+    * ``triangle`` or ``triangle_from_twiss`` a triangle distribution for laser-plasma acceleration related applications.
       A ramped, triangular current profile with a Gaussian energy spread (possibly correlated).
       The transverse distribution is a 4D waterbag.
 

examples/fodo/input_fodo_twiss.in

@@ -6,7 +6,7 @@ beam.units = static
 beam.kin_energy = 2.0e3
 beam.charge = 1.0e-9
 beam.particle = electron
-beam.distribution = waterbag_from_cs
+beam.distribution = waterbag_from_twiss
 beam.alphaX = -1.5905003499999992
 beam.alphaY = 1.5905003499999992
 beam.alphaT = 0.0

src/initialization/InitDistribution.cpp

@@ -266,19 +266,14 @@ namespace impactx
         pp_dist.get("distribution", distribution_type);
 
         std::string base_dist_type = distribution_type;
-        // Position of the underscore for splitting off the suffix in case the distribution name either ends in "_from_twiss" or "_from_cs"
+        // Position of the underscore for splitting off the suffix in case the distribution name either ends in "_from_twiss"
         std::size_t str_pos_from_twiss = distribution_type.rfind("_from_twiss");
-        std::size_t str_pos_from_cs = distribution_type.rfind("_from_cs");
         bool initialize_from_twiss = false;
 
         if (str_pos_from_twiss != std::string::npos) { // "_from_twiss" is found
             // Calculate suffix and base type, consider length of "_from_twiss" = 12
             base_dist_type = distribution_type.substr(0, str_pos_from_twiss);
             initialize_from_twiss = true;
-        } else if (str_pos_from_cs != std::string::npos) { // "_from_cs" is found
-            // Calculate suffix and base type, consider length of "_from_cs" = 8
-            base_dist_type = distribution_type.substr(0, str_pos_from_cs);
-            initialize_from_twiss = true;
         }
 
         /* After separating a potential suffix from its base type, check if the base distribution type is in the set of