Kernel functions(SPEI)
Kernel functions()所属R语言包：SPEI
Time kernel for computing the SPEI at different time scales.
时间内核计算SPEI在不同的时间尺度。
译者：生物统计家园网 机器人LoveR
描述----------Description----------
Function kern is used internally by spei and spifor computing drought indices at different time scales.
内部使用功能kern的spei和spi不同时间尺度的干旱指数计算。
用法----------Usage----------
kern(scale, type = 'rectangular', shift = 0)
kern.plot(scale = 12, shift = 0)
参数----------Arguments----------
参数：scale
numeric, time scale or length of the kernel.
数字，时间尺度或长度的内核。
参数：type
character, shape of the kernel function.
字符，形状的核函数。
参数：shift
numeric, shifting of the kernel peak.
数值，变速内核峰。
Details
详细信息----------Details----------
Drought indices, such as the SPEI or the SPI, are usually computed at different time scales to adapt to the different response times of systems affected by drought. This is acomplished by applying a kernel function to the data prior to computation of the SPEI. Aplication of a kernel has the effect of smoothing the temporal variability of the resulting SPEI, allowing for the major patterns to emerge from the noise. Other way of considering it is that the kernel allows incorporating information of previous time steps into the calculation of the current time step, so the resulting values of the SPEI adapt to the memory of the system under study.
干旱指标，如SPEI或SPI，通常会计算在不同的时间尺度，以适应不同的响应时间受干旱影响的系统。这是通过施加一个内核函数的数据事先计算的SPEI acomplished。内核金晓鸿，具有平滑所得SPEI时空变异的影响，允许的主要模式，从噪声出现。考虑它的其他方式是内核允许将以前的时间到当前时间步长的计算步骤的信息，所以所得到的值的SPEI适应所研究的系统的存储器中。
The most common kernel function is rectangular, i.e. all the data of the previous n time steps are given equal weight. This was the way the Standardized Precipitation Index (SPI) was defined, and it is also the way the SPEI is computed. This would be the default option for the kern function. However, data from the past can be thought of as having a decreasing influence in the current state of the system as the temporal lag between them increases. The function kern allows weighting the past data as a function of the time lapse, according to a series of pre-defined shapes. Available options are 'rectangular' (default), 'triangular', 'circular' and 'gaussian'.
最常见的核函数是矩形的，也就是说，所有的数据的前n个时间步长给出相同的权重。这是索引（SPI）的标准化降水被定义的方式，并且它也是SPEI计算。这将是的默认选项kern功能。然而，从过去的数据也可以被认为是在当前状态下的系统中具有减少的影响，作为它们之间的增加的时间滞后。的功能kern允许加权的过去的数据的函数的时间流逝，根据一系列的预定义的形状。可用的选项有“长方形”（默认），“三角”，“通知”和“高斯”。
By default the highest weight will be given to the observation of the current month. However, it is possible to modify this by setting the shift parameter to a value higher than zero. This will cause the highest weight be given to the n antecedent observation.
默认情况下，最高的权重将得到当前月的观察。但是，它是可能的修改此shift参数通过设置到一个大于零的值。这将导致n个先前观察，被给予最高权重。
kern.plot produces plots of the weighting factor against the time lag for the four different kernel shapes so they can be compared.
kern.plot对的时间间隔为四个不同的内核形状图的加权系数，使他们能够相比。
值----------Value----------
A vector of lenght equal to scale with weights used for computing the drought index.
一个向量的长度等于scale用于计算干旱指数的权重。
（作者）----------Author(s)----------
Santiago Beguer铆a
参考文献----------References----------
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。
注2：由于是机器人自动翻译，难免有不准确之处，使用时仔细对照中、英文内容进行反复理解，可以帮助R语言的学习。
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发表于 2012-9-30 14:58:01
