tremolo: 4/4 time, 2 half notes, single-slash tremolo question

[Kenneth Wolcott]

Hi;

  I was able to generate two half-note, single-slashed tremolos in 4/4
time using the colon syntax, but do not understand how to get the same
effect with the repeat tremolo syntax:

  \repeat tremolo 2 <b d' fs'>8 \repeat tremolo 2 <b d' fs'>8  | % m01
  <b d' fs'>2:8 q:8                                 | % m02

bar #2 is correct where bar #1 results in the following bar check warning:

Swan_Lake.ly:110:64: warning: barcheck failed at: 1/2
  \repeat tremolo 2 <b d' fs'>8 \repeat tremolo 2 <b d' fs'>8
                                                               | % m01

I'd like to use the repeat tremolo syntax because I'd like midi output
to reflect the tremolo where the colon syntax is not understood for
midi output.

  I'm apparently not doing the math correctly.

  4/4 time, half notes, two 8th note tremolos

Thanks,
Ken Wolcott