varExp(nlme)
varExp()所属R语言包：nlme
Exponential Variance Function
指数方差函数
译者：生物统计家园网 机器人LoveR
描述----------Description----------
This function is a constructor for the varExp class, representing an exponential variance function structure. Letting v denote the variance covariate and s2(v) denote the variance function evaluated at v, the exponential variance function is defined as s2(v) = exp(2* t * v), where t is the variance function coefficient. When a grouping factor is present, a different t is used for each factor level.
此功能一个varExp类代表指数的方差函数结构，构造。让v表示协方差和s2(v)表示v方差函数的计算，指数的方差函数定义为s2(v) = exp(2* t * v)t是方差函数的系数。当一个分组因素是存在的，不同的t用于每个因子水平。
用法----------Usage----------
varExp(value, form, fixed)
参数----------Arguments----------
参数：value
an optional numeric vector, or list of numeric values, with the variance function coefficients. Value must have length one, unless a grouping factor is specified in form. If value has length greater than one, it must have names which identify its elements to the levels of the grouping factor defined in form. If a grouping factor is present in form and value has length one, its value will be assigned to all grouping levels. Default is numeric(0), which results in a vector of zeros of appropriate length being assigned to the coefficients when object is initialized (corresponding to constant variance equal to one).
一个可选的数字向量，或数值的列表，与方差函数系数。 Value必须有一个长度，除非在form指定分组因素。如果value有长度大于一，它必须有form定义分组因素水平确定其元素的名称。如果一个分组因素是目前在form和value有一个长度，其价值将被分配到所有的分组级别。默认是的numeric(0)，这导致一个系数时object初始化被分配到适当的长度为零的向量（对应常数方差等于一）。
参数：form
an optional one-sided formula of the form ~ v, or ~ v | g, specifying a variance covariate v and, optionally, a grouping factor g for the coefficients. The variance covariate must evaluate to a numeric vector and may involve expressions using ".", representing a fitted model object from which fitted values (fitted(.)) and residuals (resid(.)) can be extracted (this allows the variance covariate to be updated during the optimization of an object function). When a grouping factor is present in form, a different coefficient value is used for each of its levels. Several grouping variables may be simultaneously specified, separated by the * operator, like in ~ v | g1 * g2 * g3. In this case, the levels of each grouping variable are pasted together and the resulting factor is used to group the observations. Defaults to ~ fitted(.) representing a variance covariate given by the fitted values of a fitted model object and no grouping factor.
可选片面公式的形式~ v或~ v | g，指定方差协v“，可以选择，分组因素g系数。协方差必须评估一个数值向量，并使用"."，代表拟合模型拟合值（fitted(.)）残差（resid(.)）可以被提取的对象，从中（这可能涉及表达允许方差协将在目标函数的优化更新）。当一个分组的因素是目前在form，不同系数的值用于每个级别。可以同时指定几个分组变量，分离，像*~ v | g1 * g2 * g3运营商。在这种情况下，每个分组变量的水平都粘在一起，由此产生的因素是用来组的意见。默认为~ fitted(.)代表方差协变量的拟合模型对象，并没有分组因素的拟合值。
参数：fixed
an optional numeric vector, or list of numeric values, specifying the values at which some or all of the coefficients in the variance function should be fixed. If a grouping factor is specified in form, fixed must have names identifying which coefficients are to be fixed. Coefficients included in fixed are not allowed to vary during the optimization of an objective function. Defaults to NULL, corresponding to no fixed coefficients.
一个可选的数字向量，或数值，指定其中的部分或全部方差函数的系数应该是固定的值列表。如果一个分组因素是指定在form，fixed必须有确定哪些系数是固定的名称。系数包括fixed不允许不同的目标函数的优化过程中的。默认NULL，没有固定的系数。
值----------Value----------
a varExp object representing an exponential variance function structure, also inheriting from class varFunc.
一个varExp对象，表示指数方差函数的结构，也继承从类varFunc。
作者（S）----------Author(s)----------
Jose Pinheiro and Douglas Bates <a href="mailto:bates@stat.wisc.edu">bates@stat.wisc.edu</a>
参考文献----------References----------
in S and S-PLUS", Springer.
参见----------See Also----------
varClasses, varWeights.varFunc,
varClasses，varWeights.varFunc
举例----------Examples----------
vf1 <- varExp(0.2, form = ~age|Sex)
转载请注明:出自 生物统计家园网(http://www.biostatistic.net)。
注：
注1：为了方便大家学习，本文档为生物统计家园网机器人LoveR翻译而成，仅供个人R语言学习参考使用，生物统计家园保留版权。
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发表于 2012-2-17 10:17:05
