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Van der Waerden's permanent conjecture (Theorem)

Let $A$ be any doubly stochastic $n\times n$ matrix (i.e. nonnegative real entries, each row sums to 1, each column too, hence square).

Let $A^\circ$ be the one where all entries are equal (i.e. they are $\mathord{\mathchoice {\T{1\over n}} {\T{1\over n}} {\S{1\over n}} {\SS{1\over n}}}$). Its permanent works out to

\begin{displaymath} \mathop{\rm per}\nolimits A^\circ \;=\; n!(\mathord{\mathcho... ...T{1\over n}} {\T{1\over n}} {\S{1\over n}} {\SS{1\over n}}})^n \end{displaymath}

and Van der Waerden conjectured in 1926 that this is the smallest value for the permanent of any doubly stochastic $A$, and is attained only for $A=A^\circ$:
\begin{displaymath} \mathop{\rm per}\nolimits A \;\gt\; n!(\mathord{\mathchoice ... ...ver n}} {\SS{1\over n}}})^n \quad\hbox{(for $A \ne A^\circ$).} \end{displaymath}

It was finally proven independently by Egorychev and by Falikman, in 1979/80.

Bibliography

Hal86
MARSHALL J. HALL, JR., Combinatorial Theory (2nd ed.),
Wiley 1986, repr. 1998, ISBN0471091383 and 0471315184
has a proof of the permanent conjecture.



"Van der Waerden's permanent conjecture" is owned by marijke.
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Other names:  permanent conjecture
Keywords:  doubly stochastic matrix
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Cross-references: conjecture, permanent, real, matrix, doubly stochastic
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This is version 2 of Van der Waerden's permanent conjecture, born on 2005-04-08, modified 2005-04-08.
Object id is 6935, canonical name is VanDerWaerdensPermanentConjecture.
Accessed 2298 times total.

Classification:
AMS MSC15A51 (Linear and multilinear algebra; matrix theory :: Stochastic matrices)
 15A15 (Linear and multilinear algebra; matrix theory :: Determinants, permanents, other special matrix functions)

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question about doubly stochastic matrices by mathforever on 2005-04-09 11:43:15
I am just wondering about the following question.

In the entry "Van der Waerden's permanent conjecture", i.e. the entry where this message is posted it is written that

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Let $A$ be any doubly stochastic $n\times n$ matrix (i.e. nonnegative real entries, each row sums to 1, each column too, hence square).
-----

and it is somehow suggested that doubly stochastic matrices are ALWAYS square. Is it really the case that there is NO doubly stoch. matr. (m by n) with m\neq n?

Serg.
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