# [R] Population growthrate with Euler-Lotka

Mark Christjani m_christjani at gmx.de
Mon Jun 30 09:39:45 CEST 2014

```   Hi everybody,

I`m Mark and I do my PhD in biology. I try using R to calculate a population
growth rate of animals grown on different types of food. Our workgroup has a
R-skript to do so, but sadly nobody, who knows how this works. I`ve never
used R before, but got some stuff figured out myself. The skript goes:

setwd("c:/Mark")
table
x <- c(table\$x)
L <- c(table\$lx)
m <- c(table\$mx)
r.range<- c(0, 5)
eulerlotka <- function(r) sum(L * m * exp(-r * x)) - 1
res <- uniroot(f = eulerlotka, interval = r.range, tol = 1e-8)
res\$root

I understood that the first 3 lines are simply to load my data and show it
in the workspace console. The next 4 lines define variables of my .csv table
for R. Thus far, everything works fine. Now comes the Euler-Lotka equation,
but somehow, this does not seem to work out as supposed. I tried to find a
solution on the internet, but I think this formula is somewhat special so I
could not find a suitible solution for my special problem. The console says:

> setwd("c:/Mark")
>
>
> table
V1
1     x;lx;mx
2       1;1;0
3       2;1;0
4       3;1;0
5       4;1;0
6       5;1;0
7       6;1;0
8       7;1;0
9       8;1;0
10      9;1;0
11     10;1;0
12 11;0.2;3.5
>
> x <- c(table\$x)
> L <- c(table\$lx)
> m <- c(table\$mx)
> r.range<- c(0, 5)
>
> eulerlotka <- function(r) sum(L * m * exp(-r * x)) - 1
> res <- uniroot(f = eulerlotka, interval = r.range, tol = 1e-8)
Error in uniroot(f = eulerlotka, interval = r.range, tol = 1e-08) :
f() values at end points not of opposite sign
>
> res\$root

Does anybody have an idea how to get this running?