Teaching Turtles To Reverse In Netlogo: A Guide

To make a turtle go backwards in NetLogo, you can use the 'forward' primitive, which is a turtle command that makes the selected turtle move forward in a straight line for a specified number of units. To make the turtle go backwards, you can input a negative number for the number of units, which will cause the turtle to move backwards on a straight path. For example, ask turtles [forward -2] or ask turtle 0 [fd -3.35] will make the turtle(s) move backwards.

Using the back primitive

The back primitive in NetLogo is used to make a turtle move backward by a specified number of steps. The syntax for this primitive is "bk" followed by the number of steps you want the turtle to move. For example, "bk 10" would move the turtle backward by 10 steps.

It is important to note that turtles using the back primitive can only move a maximum of one unit per time increment. So, "bk 0.5" and "bk 1" would both take one unit of time, but "bk 3" would take three units of time.

If the turtle cannot move backward the specified number of steps due to the current topology, it will complete as many steps as possible and then stop.

The back primitive is often used in conjunction with the forward primitive to control the movement of turtles in a NetLogo model. By combining these primitives, you can make turtles move forward and backward, change direction, and navigate the environment in your simulation.

In addition to the back primitive, there are other related primitives in NetLogo that you can use to control turtle movement, such as "jump", "can-move?", "forward", and "right" or "left" to change the turtle's heading.

Using the forward primitive with negative numbers

The forward primitive is a turtle primitive that makes the turtle move forward on a straight patch for a provided number of units. The shorthand version of this primitive is "fd".

When using the forward primitive, you can provide both integers (e.g., 48, -4) and floating-point numbers (e.g., 0.05, -6.23, 3.14159).

If you provide negative numbers, the turtle will move backward on a straight path.

You can also provide a variable instead of a specific number, such as "ask turtles [forward speed]".

A turtle will always maintain its straight path with the forward primitive.

If you ask a turtle to move forward in a way that requires it to move beyond the edge of the NetLogo world, there are two possible outcomes:

• If the world wrapping is turned on, which is the default setting in new NetLogo models, your turtle will leave the world on one edge and enter it again from the opposite edge.
• If the world wrapping is turned off (through the Settings menu), your turtle will move all the way to the world's edge and then get stuck there unless you change its direction with either the right or left primitives or by using the set primitive to change its heading parameter.

In NetLogo, the back primitive is used to make a turtle move backward, and it is abbreviated as "bk". If a negative number is provided to the back primitive, the turtle will move forward.

Using the jump primitive

The jump primitive in NetLogo is used to make a turtle move forward by a specified number of units. Unlike the forward primitive, the turtle moves by the specified number of units all at once, rather than one step at a time. This means that the jump primitive is faster than the forward primitive.

Ask turtles [ jump 10 ]

The above code will make all the turtles jump forward by 10 units.

The jump primitive can also take negative numbers as input. For example:

Ask turtles [ jump -10 ]

The above code will make all the turtles jump backward by 10 units.

It is important to note that if the turtle cannot jump the specified number of units due to constraints in the current topology, the turtle will not move at all.

Ask turtles [ jump 5 set color blue set size 5 ]

In this example, the turtles will jump forward by 5 units, change their color to blue, and increase their size to 5 units.

The jump primitive is a powerful tool in NetLogo that allows you to control the movement of turtles in your model.

Using the set primitive to change the heading parameter

To make a turtle go backwards in NetLogo, you can use the "forward" primitive, providing a negative number as the input. This will make the turtle move backwards on a straight path.

Now, to specifically address using the "set" primitive to change the heading parameter:

The "set" primitive in NetLogo is used to change the value of a variable to a new value. It can be used to modify global variables, local variables, and agent characteristics. One of the agent characteristics that can be changed using "set" is the "heading" parameter, which determines the direction the turtle is facing. By changing the heading, you can control the direction in which the turtle moves.

For example, let's say you have a turtle that you want to move in a specific direction, but it is currently facing the wrong way. You can use the "set" primitive to change its heading and make it face the desired direction. The code might look something like this:

Set heading 90

This code snippet will make the turtle face east, assuming the default coordinate system where east is at 90 degrees. Now, when you use the "forward" primitive, the turtle will move in the new direction.

You can also use the "set" primitive to change the heading of a turtle dynamically based on certain conditions or events in your simulation. For example, you might have a turtle that needs to change direction when it reaches the edge of the world or when it encounters an obstacle. In these cases, you can use conditional statements and the "set" primitive to adjust the heading accordingly.

Here's an example of how you might change the heading when the turtle reaches the edge of the world:

If (xcor = max-pxcor or xcor = min-pxcor or ycor = max-pycor or ycor = min-pycor) [

Set heading heading + 180

]

This code checks if the turtle has reached the left, right, top, or bottom edge of the world. If any of these conditions are true, the "set" primitive is used to change the heading by adding 180 degrees, which will make the turtle turn around and face the opposite direction.

By using the "set" primitive to change the heading parameter, you can have precise control over the direction your turtles are facing and, consequently, the paths they take as they move forward or backward in your NetLogo simulation.

Using the right and left primitives

The primitives 'right' and 'left' are used to turn a turtle a certain number of degrees to the right or left, respectively. The number of degrees can be between 0 and 360, and can be an integer or a floating-point number. For example, to turn a turtle 90 degrees to the right, you would use the code:

Ask turtles [ right 90 ]

You can also use negative numbers to turn the turtle in the opposite direction. For example, using a negative number with the 'right' primitive will turn the turtle to the left, and vice versa. So, the code:

Ask turtles [ right -90 ]

Will turn the turtle 90 degrees to the left.

The 'right' and 'left' primitives can be used to change the direction of a turtle that has reached the edge of the NetLogo world and is stuck. For example, if world wrapping is turned off, a turtle will move to the edge of the world and get stuck unless you change its direction using the 'right' or 'left' primitives.

In addition to the 'right' and 'left' primitives, you can also use the 'set' primitive to change the heading of a turtle.

Frequently asked questions