排序方式: 共有12条查询结果,搜索用时 15 毫秒
11.
We propose a method for selecting edges in undirected Gaussian graphical models. Our algorithm takes after our previous work, an extension of Least Angle Regression (LARS), and it is based on the information geometry of dually flat spaces. Non-diagonal elements of the inverse of the covariance matrix, the concentration matrix, play an important role in edge selection. Our iterative method estimates these elements and selects covariance models simultaneously. A sequence of pairs of estimates of the concentration matrix and an independence graph is generated, whose length is the same as the number of non-diagonal elements of the matrix. In our algorithm, the next estimate of the graph is the nearest graph to the latest estimate of the concentration matrix. The next estimate of the concentration matrix is not just the projection of the latest estimate, and it is shrunk to the origin. We describe the algorithm and show results for some datasets. Furthermore, we give some remarks on model identification and prediction. 相似文献
12.
Yoshihiro Yamada 《Researches on Population Ecology》1995,37(1):9-21
A revised key-factor analysis was presented for analyzing the temporal changes in the ratio of insect absolute number to plant
resource. Ten data sets for 5 insect species were then analyzed. In this key-factor analysis, the key factor is defined as
the factor contributing highly to between-year variation inR
r
, the log rate of the inter-year change of the insect-plant ratio. The yearly change of plant resource was handled as a separate
factor, expressed byr
pl
, log ratio of plant resource in yearn to plant resource in yearn+1. The following was revealed: 1) In 7 of the 10 data sets examined,r
pl
influenced variations ofR
r
; in particular in 3 casesr
pl
was the main key factor. 2) Generation-to-generation fluctuations of absolute insect densities showed density dependence
in 4 cases, while those of insect-plant ratios, in 8 cases. 3) The Royama model or a linear model, explained well the relationship
between log insect-plant ratio (X
r
) andR
r
and the relationship betweenX
r
and log yearly change rate of absolute insect density (R
abs
). However, in the 7 cases in whichr
pl
was a critical factor for variations ofR
r
, with, increase ofX
r
,R
r
showed a steeper, decrease around the equilibrium point (the point for whichR
r
is 0) thanR
abs
. This occurred becauser
pl
tended to be negatively correlated withX
r
. Consequently, in two casesX
r
fluctuated cyclicly or chaotically although without the changes in plant resource, fluctuations ofX
r
would be damped oscillations approaching equilibrium. 相似文献