Question

I have some formulas that I have defined as functions.

I’ve then ‘named’ them using particular parameters as I then need to use the output in further formula’s which makes it easier and neater.

I now need to loop the defined function to give the outputs for each month over the year, and when I put in the name of the function into the while loop, it just gives me the one answer 12 times over, but when I put the full function into the loop it works.

Is there a way that I can loop the function by using it’s name because as my formulae are progressing, they’re getting more and more complex and the code is getting busy and confusing.

def growPOP(p, T, r, K):
    #formula to calculate the new population at the end of a month.
    #p = initial population, T = total initial population
    #r = growth rate per time, K = carrying capacity
    GrPp = p + ((p * r)*((K - T) / K))
    return(GrPp)

def rt(a, b, t):
    #formula to calculate growth rate for brown fish
    #a & b are constants given, t = the month number
    rt = a + (b*sin(((2*pi)*t)/12))
    return rt

ca = 0.052
cb = 0.132   
brownPOP = 19000
goldPOP = 4400
totalPOP = brownPOP + goldPOP
carryK = 104800
redcarryK = 0.998
newcarryK = (carryK*redcarryK) + (ep/10) #ep is an input figure - for now it's 0.
month = 1
brownGrowth = growPOP(brownPOP, totalPOP, rt(ca, cb, month), carryK)

while month <= 2:
    print "Month ", month
    print "Grown brown fish: ", growPOP(brownPOP, totalPOP, rt(ca, cb, month), carryK)
    brownPOP = endbrownPOP
    goldPOP = endgoldPOP
    totalPOP = endtotalPOP
    carryK = newcarryK
    month = month + 1

So in the above loop it gives me exactly the output I want, but I really want the loop to say “print “Grown brown fish: “, brownGrowth” and still work.

There are other formulae to get brownPOP to endbrownPOP but there’s quite a few and they work, so I didn’t think they needed to be entered in to complicate things.

Answer 1

I think you just forgot to recalculate brownGrowth in every loop iteration?

brownGrowth = growPOP(brownPOP, totalPOP, rt(ca, cb, month), carryK) 
while month <= 2: 
    print "Month ", month 
    print "Grown brown fish: ", brownGrowth
    brownPOP = endbrownPOP  
    goldPOP = endgoldPOP  
    totalPOP = endtotalPOP  
    carryK = newcarryK  
    month = month + 1  

Move the brownGrowth = formula line to inside while loop:

while month <= 2: 
    brownGrowth = growPOP(brownPOP, totalPOP, rt(ca, cb, month), carryK) 
    print "Month ", month 
    print "Grown brown fish: ", brownGrowth
    brownPOP = endbrownPOP 
    goldPOP = endgoldPOP 
    totalPOP = endtotalPOP 
    carryK = newcarryK 
    month = month + 1