[R] Calculate the area under a curve

[Jeff Newmiller]

Read ?predict, paying particular attention to the newdata argument.
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Sent from my phone. Please excuse my brevity.

On August 24, 2015 2:10:11 AM PDT, CarstenH <cahoff at gmx.de> wrote:
>Hi all
>
>I need to calculate the area under a curve (integral) for the following
>data
>pairs:
>
>Depth SOC	
>22.5	0.143
>28.5 	0.165	
>34.5	0.131	
>37.5	0.134	
>40.5	0.138	
>43.5 	0.107	
>46.5	0.132
>49.5 	0.175 
>52.5	0.087	
>55.5 	0.117	
>58.5	0.126	
>61.5 	0.13	
>64.5	0.122	
>67.5 	0.161	
>71.5	0.144	
>76.5 	0.146	
>82.5	0.156	
>94.5	0.132	
>
>(Table name is P)
>
>After reading the data set I assiged the collumns by:
>
>/x <- (P$Depth)
>y <- (P$SOC)
>/
>
>and decided to make a ploynominal function (3rd order):
>
>/fitP <- lm( y~poly(x,3,raw=TRUE) )/
>
>At the next step I failed. I can plot point and function but am not
>able to
>integrate the curve between e.g. depths 20 and 80.
>
>If I try:
>/
>integrand <-function(fitP1)
>  predict(y)
>integrate(integrand, lower = 25, upper = 80)/
>
>the "Conosle" opend with the message: "Source unavailable or out of
>sync"
>and
>/
>function(fitP1)
>predict(y)
>/
>)
>
>
>Would be great if somebody could help!
>
>Thanks
>
>Carsten
>
>
>
>--
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>
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