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/gist:c3787046b7e073a65f4756361891a537

Created July 17, 2016 16:26
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Expected # left turns in lattice path (0,0) to (a,b)
Raw
gistfile1.txt
left[a_, b_] :=
Sum[(
Sum[Binomial[k - 1, i],
{i, Max[0, k - b], Min[a - 1, k - 1]}
] + Binomial[k - 1, a - 1]
) 2^(a + b - 1 - k),
{k, a + b - 1}
]/2^(a + b)
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