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We present classical simulation techniques for measure once quantum
branching programs.
For bounded error syntactic quantum branching program of width $w$
that computes a function with error $delta$ we present a classical
deterministic branching program of the same length and width at most
$(1+2/(1-2delta))^{2w}$ that computes the same function.
Second technique is a classical stochastic simulation technique for
bounded error and unbounded error quantum branching programs. Our
result is that it is possible stochastically-classically simulate
quantum branching programs with the same length and almost the same
width, but we lost bounded error acceptance property.
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