Fracture toughness: Difference between revisions

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In [[mathematics]], the '''Stieltjes [[moment problem]]''', named after [[Thomas Joannes Stieltjes]], seeks necessary and sufficient conditions for a sequence {&nbsp;''m''<sub>''n''</sub>,&nbsp;:&nbsp;''n''&nbsp;=&nbsp;0,&nbsp;1,&nbsp;2,&nbsp;...&nbsp;} to be of the form
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:<math>m_n=\int_0^\infty x^n\,d\mu(x)\,</math>
 
for some measure ''&mu;''. If such a function ''&mu;'' exists, one asks whether it is unique.
 
The essential difference between this and other well-known [[moment problem]]s is that this is on a half-line <nowiki>[</nowiki>0,&nbsp;&infin;<nowiki>)</nowiki>, whereas in the [[Hausdorff moment problem]] one considers a bounded interval [0,&nbsp;1], and in the [[Hamburger moment problem]] one considers the whole line (&minus;&infin;,&nbsp;&infin;).
 
==Existence==
Let
 
:<math>\Delta_n=\left[\begin{matrix}
m_0 & m_1 & m_2 & \cdots & m_{n}    \\
m_1 & m_2 & m_3 & \cdots & m_{n+1} \\
m_2& m_3 & m_4 & \cdots & m_{n+2} \\
\vdots & \vdots & \vdots & \ddots & \vdots \\
m_{n} & m_{n+1} & m_{n+2} & \cdots & m_{2n}
\end{matrix}\right]</math>
 
and
 
:<math>\Delta_n^{(1)}=\left[\begin{matrix}
m_1 & m_2 & m_3 & \cdots & m_{n+1}    \\
m_2 & m_3 & m_4 & \cdots & m_{n+2} \\
m_3 & m_4 & m_5 & \cdots & m_{n+3} \\
\vdots & \vdots & \vdots & \ddots & \vdots \\
m_{n+1} & m_{n+2} & m_{n+3} & \cdots & m_{2n+1}
\end{matrix}\right].</math>
 
Then {&nbsp;''m''<sub>''n''</sub>&nbsp;:&nbsp;''n''&nbsp;=&nbsp;1,&nbsp;2,&nbsp;3,&nbsp;...&nbsp;} is a moment sequence of some measure on <math>[0,\infty)</math> with infinite support if and only if for all ''n'', both
 
:<math>\det(\Delta_n) > 0\ \mathrm{and}\ \det\left(\Delta_n^{(1)}\right) > 0.</math>
 
{&nbsp;''m''<sub>''n''</sub>&nbsp;:&nbsp;''n''&nbsp;=&nbsp;1,&nbsp;2,&nbsp;3,&nbsp;...&nbsp;} is a moment sequence of some measure on <math>[0,\infty)</math> with finite support of size ''m'' if and only if for all <math>n \leq m</math>, both
 
:<math>\det(\Delta_n) > 0\ \mathrm{and}\ \det\left(\Delta_n^{(1)}\right) > 0</math>
 
and for all larger <math>n</math>
 
:<math>\det(\Delta_n) = 0\ \mathrm{and}\ \det\left(\Delta_n^{(1)}\right) = 0.</math>
 
==Uniqueness==
 
There are several sufficient conditions for uniqueness, for example, [[Carleman's condition]], which states that the solution is unique if
 
:<math> \sum_{n \geq 1} m_n^{-1/(2n)} = \infty~.</math>
 
== References ==
*{{citation|first=Michael|last=Reed|first2=Barry|last2=Simon|title=Fourier Analysis, Self-Adjointness|year=1975|ISBN=0-12-585002-6|series=Methods of modern mathematical physics|volume=2|publisher=Academic Press|page=  341 (exercise 25)}}
 
[[Category:Probability theory]]
[[Category:Mathematical analysis]]
[[Category:Theory of probability distributions]]
[[Category:Mathematical problems]]

Latest revision as of 22:54, 9 November 2014

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