
Hi R experts, 
Could you please help me to fit a linear, cubic and quadratic curve in a figure? I was trying to show all these three fitting curves with different colour in one figure. 
I spent substantial time to figure it out, but I could not. 

I have given here a example and what I did for linear, but no idea for cubic and quadratic fitting curve


> dput(test)
structure(list(sp = c(4L, 5L, 9L, 12L, 14L), env = c(12L, 18L, 
20L, 17L, 15L)), .Names = c("sp", "env"), class = "data.frame", row.names = c(NA, 
-5L))
> plot(test$sp~test$env, main = "S vs. temp", xlim=c(0,20), ylim=c(0,14), ylab="S",xlab="env")
> linear<-lm(test$sp~test$env)
> quadratic<-lm(test$sp~test$env+I(test$env^2))
> #summary(quadratic)
> cubic<-lm(test$sp~test$env+I(test$env^2)+I(test$env^3))
> #summary(cubic)
> #fitting curve
> abline(linear)
> 
Here I did for linear, but now I don't how I can plot quadratic and cubic line in the figure with different colour. I further wanted to put r2 value on the top of the fitting line. 
ON linear fitting curve, I can see the line originated from left to right (cover whole x axis). I could not plot the line only within the data set. 
Would any one help me to figure it? I think it is not difficult but for me- it is really taking time. 

Thanks and waiting for your suggestions

sincerely, 
Kristi Glover


 
 		 	   		  
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