Frequently Answered Questions (F.A.Q.)

NetLogo Questions

I have a question about NetLogo programming, models, methods, and so on.

See the NetLogo F.A.Q. Wiki in the Open NetLogo Reference Wiki or the Official NetLogo F.A.Q. at the CCL website of Northwestern University.


I've (enjoyed using) (learned a lot from) (gotten big grant money with) your turtleZERO model library. Can I throw some cash your way to show my appreciation?

Certainly, and Thank you!

You can send gifts via PayPal to

What does "It's turtles, all the way down," mean?

For example: Eastern guru affirms that the earth is supported on the back of a tiger. When asked what supports the tiger, he says it stands upon an elephant; and when asked what supports the elephant he says it is a giant turtle. When asked, finally, what supports the giant turtle, he is briefly taken aback, but quickly replies "Ah, after that it is turtles all the way down."

It refers to an infinite regression belief about the nature of the universe, and to the notion of first-causes. Wikipedia has a short article about it, including other versions of the anecdote, here: "Turtles all the way down".

For me, it amusingly speaks to the nature of NetLogo models: that whatever we call them, whether nodes or people or molecules or cells or market forces, under all the trappings, everything is a turtle. So Netlogo, also, is "turtles all the way down."


How much do your services cost?, How are you paid?

The Services page contains detailed pricing information.


Do you support the work you provide?

I generally offer at least 30 days of free follow-up support for every job. And I try to give former clients the courtesey of a fast reply to any questions sent directly to me.

Licensing and Copyrights

What are the licensing terms of models developed for me by turtleZERO?

turtleZERO clients are granted a very generous license to the code and other model materials created by turtleZERO. The license grants the client permanent, non-revokable (but non-transferrable) permission to use the model in nearly any legal way, including publishing all or part of the model code as part of a larger work, (e.g. a thesis or other paper), presenting the model on a web page, and continued development of the model.

Then who owns the copyright of the work created by turtleZERO?

In order to continue to conduct my business -- that is, to be free to reuse and recycle my own code as needed, I must retain the copyright of code that I write.

Why do you need the copyright?

I need the copyright because I need to be able to reuse any part of the code I write in future projects without worry of violating a previous customer's copyright

If I were to grant the copyright on some code to a client, then re-use some of that code, and grant another client copyright for that code, the case may occur where the same code appears in the work of two different authors, each claiming copyright for that code. Then I get sued, or worse.

Then what am I paying for?

You pay for my development services, premium access to my expertise, support, and for the license to use the resulting model.

Can you explain why that's a good deal?
Why can't it be the other way around--I own the copyright, and give you a fancy license?

Very simply, if you own the copyright, and you are a university student, or employee of a university or corporation, then the copyright could be taken from you and any license I may have had dishonored.

Some organizations, such as univerisities and corporations, make it a practice to claim ownership* of the creative output of students and employees. If I were to sell the copyrights to my work to you, it could happen that your University, or your Publisher, may claim ownership of your copyright.

This may create two problems.

First, should you wish to extend or modify the project, or use the project code as the basis for another paper or project, you must first obtain the permission of the current copyright holder--your university or employer--and you may not get it.

Second, since the license I recieved from you was issued by you, and not the new copyright owner, there is no guarantee that the new owner will honor the license. So, in order for me to work with or further modify the code, I would also need to obtain the permission of the current copyright holder. Thus, it may happen that neither of us have permission to use or modify the model or code we created together!

On the other hand, by retaining the copyright, and granting you a license, some great things happen.
First, no one can steal your license. It is between you and me and is non-revokable.
Second, because of your license, you can work on the model any way you wish, without obtaining permission from anyone.
Third, if you need help, you can hire anyone you want to help you.
You even have to opportunity to hire the original programmer who created the model--me.

* Note that some universities specifically claim that they make no claims of ownership of the work of students and employees--unless that work was done using the resources of the university. It seems to me that that qualification can be a loophole for your university to claim ownership of any of your work performed at University.

  • Did you work on your project in the university library on a university-owned computer?
  • Under lights using electricity paid for by the university?
  • Taking notes using a university-supplied pencil?

Is that using University resources? I don't know, but I prefer to err on the side of caution.


Are these questions really asked all that frequently?

Not nearly as frequently as I would like! Especially "How much do your services cost?" Someday, I wish "Can I pay you extra for no reason?" will be asked frequently enough to merit inclusion here. (The answer will be "Yes!")