How to overlay two lines using the -plot- function in R

Question

I am using R version 3.6.0. I am trying to overlay 3 lines on a single plot. I have done this successfully in the past using identical code and for some reason it doesn't seem to be working. I have the following RWE:

y.l <- function(x){0.024 - 0.00004*x + 0.00001*(10-16.8764)}

y.a <- function(x){0.024 - 0.00004*x}

y.h <- function(x){0.024 - 0.00004*x + 0.00001*(20-16.8764)}

png("yplot.png")
yplot <- plot(y.l(1:800),
              type="l", lty=2, 
              xlab="x", ylab="y", main="Getting better :/",
              ylim=c(-0.025,0.025))

lines(1:800, lty=1, y.a(1:800))
lines(1:800, lty=3, y.h(1:800))
dev.off()

which produces the following plot:

For some reason it is ignoring the extra -lines()- code. Is there some obvious mistake I am overlooking after staring at a computer all day? I have done this exact same thing before and I cannot for the life of me figure it out. And yes I have expanded the y-axis to see if they were hiding above or below and they aren't.

Answer 1

Your 3 lines are plotted, it is because of your function that you can't see them. Here the output of your three function:

> head(y.a(1:800))
[1] 0.02396 0.02392 0.02388 0.02384 0.02380 0.02376
> head(y.h(1:800))
[1] 0.02399124 0.02395124 0.02391124 0.02387124 0.02383124 0.02379124
> head(y.l(1:800))
[1] 0.02389124 0.02385124 0.02381124 0.02377124 0.02373124 0.02369124

You can see that your three function give almost the same results, it because of your 0.00001*(10-16.8764) that's is basically to small to modify your output.

If you zoom enough on the plot:

yplot <- plot(y.l(1:800),
              type="l", lty=2, 
              xlab="x", ylab="y", main="Getting better :/",
              ylim=c(.023,0.024),
              xlim=c(0,30))

lines(1:800, lty=1, y.a(1:800))
lines(1:800, lty=3, y.h(1:800))

You can see the three lines:

I think you need to change the last parameter of your function if you want to see a dramatic difference between your lines.