In addition to this, there is a third variety of variables called a table field. This can hold anything except nil including functions. It is not likely to be used however in cost functions.  

Comments 

Comments can be added by using –[[text]] instead of ‘’’ OR – instead of # 
e.g. Lua 

–[[This is a comment]] 

e.g Python 

#This is a comment 

In Lua # instead gives the length of a variable e.g. #comment -> 7 

Arrays 

In Python, the position of objects in a list starts at 0. However, in Lua the convention is that arrays start with index 1.  

e.g. Lua 

 list=[0,1,2] 

list[1] = 0 

Python 

list = [0,1,2] 

list[1] = 1  

Functions 

In Lua to define a function you also need to add an end statement at the end of the function. E.g.  

function cost(turn) 

calculatedcost = turn:length2D() 

return calculatedcost 

end 

Note that when a cost function is coded in Lua language, Lua does not allow a variable name to be the same as the name of any function inside the cost function. 

Classes 

In Python classes are used to define a group of functions which act on a particular object. For instance turn.getName() runs the function getName for the object turn for which the function has been defined. In Lua, you need to instead use a : e.g. turn:getName().  

Example of a Lua Dynamic Cost Function for Aimsun Next 

Let’s now put all the above in practice by writing a full cost function that computes a generalised cost by taking into account travel time, tolls and operating cost.  

<<code>> 

function distance(context,manager,section,turn,travelTime) 

linkdistance = turn:length2D()+section:length2D() 

return linkdistance 

end 

function cost(context, manager, section, turn, travelTime) 

— link travel time 

linkcost = turn:getStaTravelT(manager) 

— add attractiveness term 

linkcost = linkcost * (1+manager:getAttractivenessWeight()*(1-turn:getAttractiveness()/manager:getMaxTurnAttractiveness())) 

—  add user defined term 

linkcost = linkcost + manager:getUserDefinedCostWeight()*section:getUserDefinedCost() 

VOT = 30 –pence per minute 

VOC = 20 — pence per km 

linkdistance=distance(context, manager, section, turn, travelTime) 

— make generalised cost 

linkcost = linkcost + (linkdistance *VOC/VOT) +(section:getUserDefinedCost()/VOT) 

return linkcost 

end 

<<code>>