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In [[mathematics]], a sequence {{math| ''a'' = (''a''<sub>0</sub>, ''a''<sub>1</sub>, ..., ''a''<sub>''n')'</sub>}} of nonnegative real numbers is called a '''logarithmically concave sequence''', or a '''log-concave sequence''' for short, if {{math|''a''<sub>''i''</sub><sup>2</sup> ≥ ''a''<sub>''i''−1</sub>''a''<sub>''i''+1</sub>}} holds for {{math|0 < ''i'' < ''n'' }}.
'''Remark:''' some authors (explicitely or not) add two further hypotheses in the definition of log-concaves sequences:
* {{math|''a''}} is non-negative
* {{math|''a''}} has no internal zeros; in other words, the support of {{math|a}} is a connected interval of {{math|'''Z'''}}.
For instance, the sequence {{math|(1,1,0,0,1)}} checks the inequalities but not the internal zeros condition.
Examples of log-concave sequences are given by the [[binomial coefficient]]s along any row of [[Pascal's triangle]].
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