我正在尝试编写一个基本函数,以便使用nls
将一些最合适的线添加到绘图中。
除非数据恰好恰好是由传递给nls
的公式精确定义的,否则这将正常工作。我知道了这些问题,并且这已记录为as reported here行为。
我的问题是,无论模型确切描述的数据如何,我如何绕开它并强制绘制一条最佳拟合线?有没有办法检测数据是否完全匹配并绘制出完美拟合的曲线?我当前躲闪的解决方案是:
#test data
x <- 1:10
y <- x^2
plot(x, y, pch=20)
# polynomial line of best fit
f <- function(x,a,b,d) {(a*x^2) + (b*x) + d}
fit <- nls(y ~ f(x,a,b,d), start = c(a=1, b=1, d=1))
co <- coef(fit)
curve(f(x, a=co[1], b=co[2], d=co[3]), add = TRUE, col="red", lwd=2)
失败并显示错误:
Error in nls(y ~ f(x, a, b, d), start = c(a = 1, b = 1, d = 1)) :
singular gradient
我适用的简单解决方法是对数据进行
jitter
编码,但这似乎具有破坏性和缺陷。# the above code works after doing...
y <- jitter(x^2)
有没有更好的办法?
最佳答案
x <- 1:10
y <- x^2
f <- function(x,a,b,d) {(a*x^2) + (b*x) + d}
fit <- nls(y ~ f(x,a,b,d), start = c(a=1, b=0, d=0))
Error in nls(y ~ f(x, a, b, d), start = c(a = 1, b = 0, d = 0)) :
number of iterations exceeded maximum of 50
library(minpack.lm)
fit <- nlsLM(y ~ f(x,a,b,d), start = c(a=1, b=0, d=0))
summary(fit)
Formula: y ~ f(x, a, b, d)
Parameters:
Estimate Std. Error t value Pr(>|t|)
a 1 0 Inf <2e-16 ***
b 0 0 NA NA
d 0 0 NA NA
---
Signif. codes: 0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ‘ ’ 1
Residual standard error: 0 on 7 degrees of freedom
Number of iterations to convergence: 1
Achieved convergence tolerance: 1.49e-08
请注意,我必须调整起始值,结果对起始值很敏感。
fit <- nlsLM(y ~ f(x,a,b,d), start = c(a=1, b=0.1, d=0.1))
Parameters:
Estimate Std. Error t value Pr(>|t|)
a 1.000e+00 2.083e-09 4.800e+08 < 2e-16 ***
b -7.693e-08 1.491e-08 -5.160e+00 0.00131 **
d 1.450e-07 1.412e-08 1.027e+01 1.8e-05 ***
---
Signif. codes: 0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ‘ ’ 1
Residual standard error: 6.191e-08 on 7 degrees of freedom
Number of iterations to convergence: 3
Achieved convergence tolerance: 1.49e-08
关于r - nls最合适的线-如何强制绘制线?,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/13945045/