Question:

I am calculating cumulative turtle mortality in netlogo as a function of distance moved by turtles (100 of them) from the origin (start-patch) in the netlogo interface world. In the code below the 'Pass-Away' procedure is linked to a global interface switch called "space-death" which when switched on yields said distance-based mortality undertaken by the procedure called "Pass-Away-Space", otherwise maintains regular per-time-step (tick) mortality undertaken by the procedure called "Pass-Away-Time":

to Pass-Away-Time ask turtles [ let chances 1 - exp( -1 * mortality * ticks ) if chances >= 1 [die set dead-count dead-count + 1 ] ] end to Pass-Away-Space ask turtles [ let chances 1 - exp( -1 * mortality * [distance start-patch] of turtles) if chances >= 1 [die set dead-count dead-count + 1 ] ] end to Pass-Away ask turtles [ ifelse space-death [ Pass-Away-Space][ Pass-Away-Time ] ] end

I get two errors doing this, both likely due to issues with the coding of the "Pass-Away-Space" procedure. The first is <em>Only the observer can ASK the set of all turtles.</em> Then when I move the let chances 1 - exp( -1 * mortality * [distance start-patch] of turtles) outside of the ask turtles[] brackets this error is resolved only yield another that says ** expected input to be a number but got the list* followed by a sequence of numbers. Perhaps due to the fact that the section of the mortality equation that reads * [distance start-patch] of turtles is invoked for multiple turtles (which is exactly what I want to achieve - have each random-walking turtle use its distance from the origin to calculate its cumulative per-step mortality and die above a threshold - an event that occurs at different times for different turtles at different distances). Any thoughts on how to resolve this?

The first error is because you are asking all turtles to ask all turtles. Starting with your Pass-Away procedure and assuming space-death is set to TRUE. What happens? You ask all turtles to run the Pass-Away-Space procedure. That is, each turtle will run that procedure in turn. The first step of that procedure is to ask turtles [ ]. So a turtle is asking all turtles to do something. Hence the error.

To fix it, you need to rewrite the Pass-Away-Space procedure so it runs whatever code needs to be run for a SINGLE turtle (and similarly for Pass-Away-Time). You probably want something like:

to Pass-Away-Space if exp( -1 * mortality * [distance start-patch]) < 0 [ die set dead-count dead-count + 1 ] end

So the first issue here is the nested use of the ask turtles [ ... ] command, which we can disambiguate by removing it from the to Pass-Away procedure or alternatively, from both of the other two (preceding) functions nested within it, as seen below (demonstrating the later of the aforementioned means.

let start-patch patch 0 0 to Pass-Away-Time ask turtles [ let chances 1 - exp( -1 * mortality * ticks ) if chances >= 1 [die set dead-count dead-count + 1 ] ] end to Pass-Away-Space ask turtles [ ; let chances 1 - exp( -1 * mortality * [distance start-patch] of turtles) let chances 1 - exp( -1 * mortality * (distance start-patch)) if chances >= 1 [die set dead-count dead-count + 1 ] ] end to Pass-Away ifelse space-death [ Pass-Away-Space][ Pass-Away-Time ] end

The second error can be resolved by switching the line of code commented (;) out in the to Pass-Away-Space procedure withe the immediate succeeding line so that when each turtle attempts to execute chances, cumulative per-distance (from origin) mortality is not calculated as an array of turtle chances with the use of the [distance start-patch] of turtles command, but rather per individual turtle with (distance start-patch) whenever the procedure is called by the nesting to Pass-Away procedure.