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Likelihood

As in the earlier situation, note that:

equation1205

Also,

equation1211

that is, tex2html_wrap_inline2887 is a deterministic function of the various parameters obtained by numerically solving the differential equation model. The ordering of coalescence determines that crack i is the tex2html_wrap_inline3215 crack to be born, and also which crack dies when crack i is born. The crack only exists at times between birth and death, and we define

equation1216

and

equation1219

The tex2html_wrap_inline3215 realisation time from a homogeneous Poisson process is gamma distributed with scale tex2html_wrap_inline3223 and shape parameter k, since it is the sum of exponentially distributed random variables.

Let tex2html_wrap_inline3227 be the number of coalescences in interval i, where interval 1 is [20,30], interval 2 is [30,40], interval 3 is [40,50] and interval 4 is [50,60] (where intervals are given in thousands of cycles). Then tex2html_wrap_inline3227 are realisations of a Poisson distribution with rate tex2html_wrap_inline3223 . That is to say the likelihood for the tex2html_wrap_inline3227 is:

equation1224

O is an ordering of the times of birth and death for the different cracks and determines which cracks coalesce. In the context of spatial data, O would obviously depend upon some parameters representing the spatial nature of the specimen, such as local microcrack density, but this data is not available here.



Cathal Walsh
Sat Jan 22 17:09:53 GMT 2000