TRUE-WORLD System Dynamics Software

//Stocks and Flows first initialization
At t = 0 {
    stocks(t) = stocks initial value
    mirror stocks(t) = sum (source stocks (t))
    flows(t) = 0
}

//-----------------------------------------------------------------------------

for t = 1 to last t { //last t = (last_cycle) x (last_time_per_cycle)

//Stocks and Flows initialization for current time unit
    stocks(t) = stocks(t-1)
    mirror stocks(t) = mirror stocks(t-1)
    flows(t) = 0

Filtering and grouping actions in Sets sorted by Chronology()

for first Set to last Set {

//Actions dynamic computing

        for first action to last action {
            y[action] = function(action code)*
        }

        for first action to last action {
            if flow[action] links two stocks {
//First stocks update
                if Rate is disable {
                    source stock(t) = source stock(t) - y[action]
                    target stock(t) = target stock(t) + y[action]
                else {
//store the return value
                    RateBuffer[action] = y[action]

}
}

//Flows update
flow[action](t) = flow[action](t) + y[action]
}

//First mirror stocks update
        for first mirror stock to last mirror stock {
            mirror stock(t) = sum (source stocks(t))
        }

}

//Last stocks update
    for first RateBuffer[action] to last RateBuffer[action] {
        source stock[action](t) = source stock[action](t) - (RateBuffer[action] / TimeStepI)
        target stock[action](t) = target stock[action](t) + (RateBuffer[action] / TimeStepI)
    } // TimeStepI = 1 / TIME STEP

//Last mirror stocks update
    for first mirror stock to last mirror stock {
        mirror stock(t) = sum (source stocks(t))
    }

}

//Algorithm end

y[action] = function(action code)*

Action code example:

//Read a current stock or flow or mirror stock value

y= Svalue("SB") + Fvalue("FE") - Mvalue("FA")

//Read a delayed value:

y+= Svalue("SB",4,10) + Fvalue("FE",2,2) - Mvalue("FA",3,5)

y+= Svalue("SB",False,31) + Fvalue("FE",False,15) - Mvalue("FA",False,40)

//Default syntax to read a current stock or flow or mirror stock value

Svalue("SB") : read the current value of the stock "SB"

Fvalue("FE") : read the current value of the flow "FE"

Mvalue("FA") : read the current value of the mirror stock "FA"

//First syntax for delayed value:

Svalue("SB",c,t) // c= cycle, t=time = current time in the current cycle

//Example:

Svalue("SB",4,10) : read a delayed value of the stock "SB" for cycle = 4 and time = 10

Fvalue("FE",2,2) : read a delayed value of the flow "FE" for cycle = 2 and time = 2

Mvalue("FA",3,5) : read a delayed value of the mirror stock "FA" for cycle = 3 and time = 5

/Second syntax for delayed value:

Svalue("SB",False,nbt) // nbt or nbtime =current time number starting from first cycle

//Example:

Svalue("SB",False,31) : read a delayed value of the stock "SB" for nbtime = 31

Fvalue("FE",False,15) : read a delayed value of the flow "FE" for nbtime = 15

Mvalue("FA",False,40) : read a delayed value of the mirror stock "FA" for nbtime = 40

// nbtime max = (last_cycle) x (last_time)

//be careful with action Chronologies !