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===The Lognormal Distribution===
#REDIRECT [[The_Lognormal_Distribution]]
 
The lognormal distribution is commonly used for general reliability analysis, cycles-to-failure in fatigue, material strengths and loading variables in probabilistic design.
When the natural logarithms of the times-to-failure are normally distributed, then we say that the data follow the lognormal distribution.
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The <math>pdf</math> of the lognormal distribution is given by:
 
::<math>\begin{align}
& f(t)=\frac{1}{t{\sigma}_{t'}\sqrt{2\pi}}e^{-\tfrac{1}{2}(\tfrac{t'-{\mu'}}{\sigma_{t'}})^2}\\
& f(t)\ge  0,t>0,{{\sigma }_{t'}}>0 \\
& {t'}=  \ln (t)
\end{align}
</math>
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where,
::<math>\begin{align}
&  {\mu'}= \text{mean of the natural logarithms of the times-to-failure} \\
&  {\sigma_{t'}}= \text{standard deviation of the natural logarithms of the times to failure} 
\end{align}</math>
 
The lognormal distribution and its characteristics are presented in more detail in [[The Lognormal Distribution |Chapter 10]].
 
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Latest revision as of 10:01, 9 August 2012