韦伯累积分布函数从“fitdistr”命令启动(Weibull cumulative distrib

我用fitdistr函数自R MASS包来调整威布尔2个参数的概率密度函数（pdf）。

这是我的代码：

require(MASS)

h = c(31.194, 31.424, 31.253, 25.349, 24.535, 25.562, 29.486, 25.680, 26.079, 30.556,      30.552, 30.412, 29.344, 26.072, 28.777, 30.204, 29.677, 29.853, 29.718, 27.860, 28.919, 30.226, 25.937, 30.594, 30.614, 29.106, 15.208, 30.993, 32.075, 31.097, 32.073, 29.600, 29.031, 31.033, 30.412, 30.839, 31.121, 24.802, 29.181, 30.136, 25.464, 28.302, 26.018, 26.263, 25.603, 30.857, 25.693, 31.504, 30.378, 31.403, 28.684, 30.655,  5.933, 31.099, 29.417, 29.444, 19.785, 29.416, 5.682, 28.707, 28.450, 28.961, 26.694, 26.625, 30.568, 28.910, 25.170, 25.816, 25.820)

weib = fitdistr(na.omit(h),densfun=dweibull,start=list(scale=1,shape=5))

hist(h, prob=TRUE, main = "", xlab = "x", ylab = "y", xlim = c(0,40), breaks = seq(0,40,5))
curve(dweibull(x, scale=weib$estimate[1], shape=weib$estimate[2]),from=0, to=40, add=TRUE)

现在，我想创建韦伯累积分布函数（CDF）和绘制它的图形：

，其中x> 0，B =刻度，=形状

我尝试应用比例和形状参数h使用上面的公式，但它不是这样。

Answer 1:

下面是在累积密度函数刺伤。你只需要记住，包括为采样点的间距的调整（注意：它适用于采样点均匀间距小于或等于1）：

cdweibull <- function(x, shape, scale, log = FALSE){
  dd <- dweibull(x, shape= shape, scale = scale, log = log)
  dd <- cumsum(dd) * c(0, diff(x))
  return(dd)
}

以上关于尽管如此，你可以绘制它在图形中的同级别差异的讨论dweibull ：

require(MASS)

h = c(31.194, 31.424, 31.253, 25.349, 24.535, 25.562, 29.486, 25.680,
      26.079, 30.556, 30.552, 30.412, 29.344, 26.072, 28.777, 30.204, 
      29.677, 29.853, 29.718, 27.860, 28.919, 30.226, 25.937, 30.594, 
      30.614, 29.106, 15.208, 30.993, 32.075, 31.097, 32.073, 29.600, 
      29.031, 31.033, 30.412, 30.839, 31.121, 24.802, 29.181, 30.136, 
      25.464, 28.302, 26.018, 26.263, 25.603, 30.857, 25.693, 31.504, 
      30.378, 31.403, 28.684, 30.655,  5.933, 31.099, 29.417, 29.444, 
      19.785, 29.416, 5.682, 28.707, 28.450,  28.961, 26.694, 26.625, 
      30.568, 28.910, 25.170, 25.816, 25.820)

weib = fitdistr(na.omit(h),densfun=dweibull,start=list(scale=1,shape=5))

hist(h, prob=TRUE, main = "", xlab = "x", 
     ylab = "y", xlim = c(0,40), breaks = seq(0,40,5), ylim = c(0,1))

curve(cdweibull(x, scale=weib$estimate[1], shape=weib$estimate[2]),
  from=0, to=40, add=TRUE)

Answer 2:

这适用于我的数据，但你可能有所不同。它采用rweibull3功能从FAdist包。

>h=rweibull3(1000,2,2,2)

>#this gives some warnings...that I ignore.
>weib = fitdistr(h,densfun=dweibull3,start=list(scale=1,shape=5,thres=0.5))

There were 19 warnings (use warnings() to see them)

要注意的一点是，开始价值产生影响的方式，配合进行。因此，如果开始值接近真实值，你会得到较少的警告。

>curve(dweibull3(   x, 
            scale=weib$estimate[1], 
            shape=weib$estimate[2], 
            thres=weib$estimate[3]),
            add=TRUE)