Merge branch '76-update-fromfile-type-distribution' into 'master'

Resolve "Update FROMFILE type distribution"

Closes #76

See merge request OPAL/documentation/manual!168

distribution.asciidoc

@@ -347,8 +347,18 @@ the type of emission model used. This is defined by the attribute
 of `NONE` for the `EMISSIONMODEL` (which is the default) can be defined
 so as not to affect the distribution coordinates at all.
 
-To maintain consistency latexmath:[N] and `NPART` from the `BEAM`
-command in Chapter link:beam-command#chp.beam-command[Beam Command] must be equal.
+To maintain consistency, latexmath:[N] and `NPART` from the `BEAM` command
+(see Chapter link:beam-command#chp.beam-command[Beam Command]) must be equal.
+In the same way, when using a `FROMFILE` type distribution, the average
+momentum of the distribution must coincide with the momentum specified in the
+`BEAM` command by means of `GAMMA`, `ENERGY` or `PC` attributes
+(see Section link:beam-command#sec.beam-command.beam-energy[Beam Energy]).
+In _OPAL-t_, the given momentum in the `BEAM` command must coincide with the
+z-component of the momentum of the particle distribution in the file.
+On the other hand, in _OPAL-cycl_ the given momentum must coincide with the
+total momentum of the particle distribution, taking into account that the
+initial distribution in _OPAL-cycl_ is always specified in the
+link:opalcycl#sec.opalcycl.localframe[local reference frame].
 
 [[sec.distribution.gaussdisttype]]
 ==== `GAUSS` Distribution Type