与nls不同，nls2将向量化的初始值视为单个元素

问题描述

我注意到我可以使用 nls 拟合参数向量，如下所示。这让我决定要设置的参数数量。如下例所示；我适合的地方 y = k + a_1 x ^ 2 + a_2 x ^ 3 + a_3 x ^ 3 。我可以简单地更改初始值的数量，这会更改要估计的系数的数量。

I noticed that I can fit parameter vector, as below, using nls. This let's me decide the number of parameters I want to fit. As in the example below; where I am fitting y = k + a_1 x^2 + a_2 x^3 + a_3 x^3. I can simply change the number of initial values, which change the number of co-efficients to estimate.

但是，这种方法不适用于 nls2 。它只是对待适合 y = k + a_1 * x 的三倍！

But, this approach doesn't work with nls2. It just treats fits the y = k + a_1 * x, three times!

我的问题是如何获得 nls2 来确定基于初始值（或类似值）的参数数量，例如 nls 。

My questions is how to get nls2 to determine the number of parameters to fit based on the initial values - or something similar - as in the case with nls.

我对 nls 或类似软件包没有太多经验。因此，我正在尝试修复。我想 nls2 比 nls ...

I don't have a lot of experience with nls or similar packages. So, I am trying to mend that. I am guessing nls2 has more capabilities than nls...

x <- c(32,64,96,118,126,144,152.5,158)
y <- c(99.5,104.8,108.5,100,86,64,35.3,15)


model_fun <- function(x, int_sep, para) {
  int_sep +  rowSums(sapply(1:length(para), function(i) para[i] * x^i))
}

使用 nls 包

With nls package

mod_nls <- nls(y ~ model_fun(x, int_sep, para),
             start = list(int_sep = 0, para=c(1, 1, 1)))

mod_nls
# Nonlinear regression model
# model: y ~ model_fun(x, int_sep, para)
# data: parent.frame()
# int_sep      para1      para2      para3
# 1.269e+02 -1.626e+00  2.910e-02 -1.468e-04
# residual sum-of-squares: 65.87
#
# Number of iterations to convergence: 1
# Achieved convergence tolerance: 1.732e-07

使用 nls2 包

With nls2 package

 mod_nls2 <- nls2(y ~ model_fun(x, int_sep, para),
                start = list(int_sep = 0, para=c(1, 1, 1)))

mod_nls2
# Nonlinear regression model
# model: y ~ model_fun(x, int_sep, para)
# data: parent.frame()
# int_sep     para
# 143.0438  -0.5966
# residual sum-of-squares: 3661
#
# Number of iterations to convergence: 1
# Achieved convergence tolerance: 7.602e-09

（编辑：我对此特定模型不感兴趣-似乎是一个简单的例子）

推荐答案

nls2 将 start = 参数转换为数据内部框架，因此如果您以 as.data.frame（as.list（start））的形式提供它（在示例中 works表示它创建了具有1行2列的数据帧，两个参数中的每一个都包含一列-请注意dat一个框架列可以容纳复杂的对象），那么您应该可以：

nls2 converts the start= argument to a data frame internally so if you provide it in a form such that as.data.frame(as.list(start)) works (where in the example "works" means it creates a data frame with 1 row and 2 columns, one column for each of the two parameters -- note that data frame columns can hold complex objects) then you should be OK:

nls2(y ~ model_fun(x, int_sep, para),
  start = list(int_sep = 0, para = I(t(c(1, 1, 1)))))

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