  We report on a lattice-QCD calculation of the B to pi l nu form factor with
domain-wall light quarks and relativistic b-quarks using the 2 + 1 flavor
domain-wall fermion and Iwasaki gauge-field ensembles generated by the RBC and
UKQCD Collaborations. We present initial results obtained from the coarser (a ~
0.11 fm) 24^3 lattices and some of the finer (a ~ 0.086 fm) 32^3 lattices.
