  We characterize the capacity region to within log{2(M-1)} bits/s/Hz for the
M-transmitter K-receiver Gaussian multicast channel with feedback where each
receiver wishes to decode every message from the M transmitters. Extending
Cover-Leung's achievable scheme intended for (M,K)=(2,1), we show that this
generalized scheme achieves the cutset-based outer bound within log{2(M-1)}
bits per transmitter for all channel parameters. In contrast to the capacity in
the non-feedback case, the feedback capacity improves upon the naive
intersection of the feedback capacities of K individual multiple access
channels. We find that feedback provides unbounded multiplicative gain at high
signal-to-noise ratios as was shown in the Gaussian interference channel. To
complement the results, we establish the exact feedback capacity of the
Avestimehr-Diggavi-Tse (ADT) deterministic model, from which we make the
observation that feedback can also be beneficial for function computation.
