使用“积分"计算两条线之间的面积时出错. [英] Error calculating the area between two lines using "integrate"

问题描述

我正在尝试使用R的integrate函数计算两个图之间的面积.我可以将两条预测曲线放在同一图上，并在两条曲线之间的区域进行阴影化以进行可视化:

I'm attempting to calculate the area between two plots using R's integrate function. I have two forecast curves that I'm able to place on the same plot and also shade in the area between the two curves, for visualisation:

x1 = seq(1,200,1)
y1 = # 200 numbers from 0.02 - 1.000
y2 = # 200 numbers from 0.00 - 0.95

plot(x1,y1,type="l",bty="L",xlab="Forecast Days",ylab="Curve Actuals")
points(x1,y2,type="l",col="red")

polygon(c(x1,rev(x1)),c(y2,rev(y1)),col="skyblue")

在此遵循示例 https://stat.ethz. ch/pipermail/r-help/2010-September/251756.html 我试图为我的数据执行相同的代码，以计算两条曲线之间的距离.如示例所述，两条曲线之间的面积与两条曲线之间的差异的积分相同(分别为其绝对值)" :

Following the example here https://stat.ethz.ch/pipermail/r-help/2010-September/251756.html I've attempted to execute the same code for my data to calculate the are between the two curves. As stated in the example "the area between two curves is the same as the integral of the difference between these two curves (resp. its absolute values)":

f1 = approxfun(x1, y1-y2)     # piecewise linear function
f2 = function(x) abs(f1(x))   # take the positive value

integrate(f2, 1, 200)

但是我遇到以下错误:

Error in integrate(f2, 1, 200) : maximum number of subdivisions reached

感谢对此的澄清.谢谢！

Appreciate any clarity that can be shed on this. Thanks!

推荐答案

如@Roland先前的注释所建议的那样，增加细分的数量可以正确执行.确实会产生绝对错误，但非常微小.

Increasing the number of subdivisions, as suggested in an earlier comment by @Roland, executes correctly. It does produce an absolute error, but very minute.

f1 = approxfun(x1, y1-y2)     # piecewise linear function
f2 = function(x) abs(f1(x))   # take the positive value

area1 = integrate(f2, 1, 200, subdivisions = 300)
> area1
9.327692 with absolute error < 8.1e-05

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