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26 Combinatorial AnalysisProperties

§26.3 Lattice Paths: Binomial Coefficients

Contents
  1. §26.3(i) Definitions
  2. §26.3(ii) Generating Functions
  3. §26.3(iii) Recurrence Relations
  4. §26.3(iv) Identities
  5. §26.3(v) Limiting Form

§26.3(i) Definitions

\genfrac{(}{)}{0.0pt}{}{m}{n} is the number of ways of choosing n objects from a collection of m distinct objects without regard to order. \genfrac{(}{)}{0.0pt}{}{m+n}{n} is the number of lattice paths from (0,0) to (m,n). See also 1.2(i). The number of lattice paths from (0,0) to (m,n), m\leq n, that stay on or above the line y=x is \genfrac{(}{)}{0.0pt}{}{m+n}{m}-\genfrac{(}{)}{0.0pt}{}{m+n}{m-1}.

26.3.1 \genfrac{(}{)}{0.0pt}{}{m}{n}=\genfrac{(}{)}{0.0pt}{}{m}{m-n}=\frac{m!}{(m-n)!%
\,n!},m\geq n,
26.3.2 \genfrac{(}{)}{0.0pt}{}{m}{n}=0,n>m.

For numerical values of \genfrac{(}{)}{0.0pt}{}{m}{n} and \genfrac{(}{)}{0.0pt}{}{m+n}{n} see Tables 26.3.1 and 26.3.2.

Table 26.3.1: Binomial coefficients \genfrac{(}{)}{0.0pt}{}{m}{n}.
m n
0 1 2 3 4 5 6 7 8 9 10
0 1
1 1 1
2 1 2 1
3 1 3 3 1
4 1 4 6 4 1
5 1 5 10 10 5 1
6 1 6 15 20 15 6 1
7 1 7 21 35 35 21 7 1
8 1 8 28 56 70 56 28 8 1
9 1 9 36 84 126 126 84 36 9 1
10 1 10 45 120 210 252 210 120 45 10 1
Table 26.3.2: Binomial coefficients \genfrac{(}{)}{0.0pt}{}{m+n}{m} for lattice paths.
m n
0 1 2 3 4 5 6 7 8
0 1 1 1 1 1 1 1 1 1
1 1 2 3 4 5 6 7 8 9
2 1 3 6 10 15 21 28 36 45
3 1 4 10 20 35 56 84 120 165
4 1 5 15 35 70 126 210 330 495
5 1 6 21 56 126 252 462 792 1287
6 1 7 28 84 210 462 924 1716 3003
7 1 8 36 120 330 792 1716 3432 6435
8 1 9 45 165 495 1287 3003 6435 12870

§26.3(ii) Generating Functions

26.3.3 \sum_{n=0}^{m}\genfrac{(}{)}{0.0pt}{}{m}{n}x^{n}=(1+x)^{m},m=0,1,\dotsc,
26.3.4 \sum_{m=0}^{\infty}\genfrac{(}{)}{0.0pt}{}{m+n}{m}x^{m}=\frac{1}{(1-x)^{n+1}},|x|<1.

§26.3(iii) Recurrence Relations

26.3.5 \genfrac{(}{)}{0.0pt}{}{m}{n}=\genfrac{(}{)}{0.0pt}{}{m-1}{n}+\genfrac{(}{)}{0%
.0pt}{}{m-1}{n-1},m\geq n\geq 1,
26.3.6 \genfrac{(}{)}{0.0pt}{}{m}{n}=\frac{m}{n}\genfrac{(}{)}{0.0pt}{}{m-1}{n-1}=%
\frac{m-n+1}{n}\genfrac{(}{)}{0.0pt}{}{m}{n-1},m\geq n\geq 1,
26.3.8 \genfrac{(}{)}{0.0pt}{}{m}{n}=\sum_{k=0}^{n}\genfrac{(}{)}{0.0pt}{}{m-n-1+k}{k},m\geq n\geq 0.

§26.3(iv) Identities

26.3.9 \genfrac{(}{)}{0.0pt}{}{n}{0}=\genfrac{(}{)}{0.0pt}{}{n}{n}=1,
26.3.11 \genfrac{(}{)}{0.0pt}{}{2n}{n}=\frac{2^{n}(2n-1)(2n-3)\cdots 3\cdot 1}{n!}.

See also §1.2(i).

§26.3(v) Limiting Form