Re: single Note swell

[Simon Albrecht]

On 20.12.2017 01:21, Vivyan wrote:
> code to instruct a swell for the duration of c2

There’s several possibilities:
First, LilyPond has the built-in command \espressivo (which is 
technically not a dynamic script, but an articulation):
%%%%%%
{ c2\espressivo }
%%%%%%

Second, your ‘example’ hints at this strategy:
%%%%%%
\context Voice <<
  { c2 }
  { s4\< s\> <>\! }
>>
%%%%%%

Third, you could use this:
%%%%%%
after =
#(define-music-function (t e m) (ly:duration? ly:music? ly:music?)
   #{
     \context Bottom <<
       #m
       { \skip $t <> -\tweak extra-spacing-width #empty-interval $e }
     >>
   #})
{ \after 8. \> \after 4. \! c2\< }
%%%%%%%

It’s up to you which you prefer.

Best,
Simon