globals
  []

patches-own
  [loan                          ;the amount of microcredit the bank can provide
  raw-materials                  ;if true there's a raw materials supplier on the patch
  ]

turtles-own
   [wealth                       ;turtles' wealth
    borrower?                    ;if true the turtle has got a microcredit loan
    debts                        ;the loan's amount
    repayment                    ;indicates if the turtle has repayed the debt
    provisions                   ;amount of raw material 
    diamonds                     ;number of bought diamonds
    produced-diamonds            ;number of produced diamonds
    producer?                    ;true if turtle has produced at least one diamond
    labor                        ;
    employed?                    ;true if turtle has worked at least once
    ]

;############################################ SETUP ############################################

to setup
  ca
  crt turtles-number
  setup-turtles
  set pcolor-of patch -16 4 green                      ;the microfinancial institution is green
  set loan-of patch -16 4 microcredit-available        ;microcredits available is set using the slider
  set raw-materials-of patch 0 16 true           
  set raw-materials-of patch 12 -8 true
  set pcolor-of patch 0 16 grey                        ;the raw materials supplier is on the grey patch
  set pcolor-of patch 12 -8 grey
 end

to setup-turtles
  set-default-shape turtles "person"
  ask turtles [
  setxy (random-float screen-size-x)
        (random-float screen-size-y)
  set wealth random 70                                 ;wealth each turtles start with is different 
  set color pink - 1
  set borrower? false
  set producer? false
  set employed? false
  set provisions 0
  set diamonds 0
  set labor 0
  ]
  
end

 
to go
 ask turtles [move]                              ;this procedure makes turtles move
 ask turtles [borrow]                            ;this procedure makes turtles get a microcredit 
 ask turtles [supplier]                          ;this procedure makes turtles buy raw materials
 ask turtles [produce]                           ;this procedure makes turtles produce diamonds
 ask turtles [trade]                             ;this procedure makes turtles buy and sell diamonds
 ask turtles [hire]                              ;this procedure makes turtles hire other turtles
 stop-loan
 update-plot
end  
 
to move  
  lt random 360
  fd random 4
end 


;############################################ MICROCREDIT ACTIVITY ############################################

to borrow
  if (wealth > loan-limit and loan > 10 and borrower? = false) [          ;the bank must have some loans available and the turtles can't already be borrowers
  set wealth (wealth + 10)
  set color green                                                         ;when turtles get the loan, they turn green
  set debts (debts + 10)
  set loan (loan - 10)
  set borrower? true
  stop-loan
  ]
  fd random 5
  repay
 end

to stop-loan
   if loan-of patch -16 4 = 10                                            ;the bank must have a minimum reserve
   [stop (borrow)]
end 

to repay
   if (borrower? = true and produced-diamonds > 6 and pcolor = green) [   ;producing diamonds, turtles can repay their debts
   set wealth (wealth - 10)
   set color white
   set debts (debts - 10)
   set repayment (repayment + 1)
   set loan-of patch -16 4 (loan-of patch -16 4 + 10)
   set borrower?  false]
end


;############################################ PRODUCTION ############################################

to supplier
  if ((borrower? = true or repayment > 0 and wealth > 40)and pcolor = grey) [      ;not every turtle can buy raw materials. They must be borrower or still have wealth > 40 after the repayment
  set provisions (provisions + 5)
  set wealth (wealth - 2)
  fd 2
  ]
end

to produce
  if (provisions > 6 and labor > 4)[                                               ;turtles must have both raw materials and labor to produce diamonds
  set diamonds (diamonds + 1)
  set provisions (provisions - 7)
  set color yellow
  set producer? true
  set produced-diamonds (produced-diamonds + 1)
  ]
 end

to hire
 if ((borrower? = true and provisions > 5) and count other-turtles-here with [employed? = false] > 0)  ;if turtles have got a loan and raw materials, they can hire other turtles
 [employ]
 end

to employ
  let worker 0
  set worker random-one-of other-turtles-here with [wealth < 30 and employed? = false]   ;if turtles are rich they don't want to work
  if worker != nobody [                                                                  ;i.e. there's an unemployed turtle around
  set labor (labor + 2)
  set labor-of worker (labor-of worker - 2)
  set wealth (wealth - 4)
  set wealth-of worker (wealth-of worker + 4)  
  set employed?-of worker true
  set color-of worker red
  ]
  end
   


;############################################ TRADING ############################################


to trade
  if ((wealth > 30 and producer? = false) and count other-turtles-here with [diamonds > 0] > 0) 
  [buy]
  end 
  
to buy
  let seller 0 
  set seller random-one-of other-turtles-here with [diamonds > 0 and producer? = true]
  if seller != nobody [
  set diamonds (diamonds + 1)
  set wealth (wealth - 11)
  set diamonds-of seller (diamonds-of seller - 1)
  set wealth-of seller (wealth-of seller + 11)
  set color blue
  ]
  end   
  
 
;############################################ REPORTS ############################################  
         
to-report total-debts
  ifelse any? turtles
  [report (sum values-from turtles  [debts])]
   [report 0]
end

to-report total-diamonds
ifelse any? turtles
  [report (sum values-from turtles  [diamonds])]
   [report 0]
end


to-report nrepayment
ifelse any? turtles
  [report (sum values-from turtles [repayment])]
  [report 0]
  end

;############################################ PLOTS ############################################
  
to update-plot
  set-current-plot "Populations"
  set-current-plot-pen "employed"
  plot count turtles with [employed?]
  set-current-plot-pen "poor"
  plot count turtles with [wealth < 20 or diamonds < 1]

  set-current-plot "Producers"
  set-current-plot-pen "producers"
  plot count turtles with [producer?]

 end
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@#$#@#$#@
WHAT IS IT?
-----------
This model simulates a small and simple economy in a poor country with a microfinance institution. The turtles start the simulation with a random level of wealth and they can then obtain a loan; if they do, they can buy raw materials, hire other turtles with a lower wealth level and produce some goods (symbolized by diamonds), which can be sold to other turtles.


HOW IT WORKS
------------
The turtles, which are all pink at the beginning, start walking with random movements; if they walk over the patch which represents the bank, if microcredit is still available, they can obtain some (and they turn green). Once they have got it, they keep on moving and, if they walk over one of the two patches standing for traders, they can buy some raw materials. 
If they do so and they meet with some turtles with a lower wealth level and no microcredit obtained, they hire them (the contractor becoming yellow and the workers red), paying a wage which contributes to improve the condition of poorer turtles.
Once they have obtained a loan, bought raw materials and hired some other turtles, the "entrepreneur turtles" start producing goods which can be sold to other turtles that have started with a higher wealth level and they're neither entrepreneurs nor workers (those buying diamonds turning blue).
By selling the products, the diamonds producers obtain a payment which repays their investments and grants them a gain, so that they can refound the loan (becoming white in this case).


HOW TO USE IT
-------------
Start the simulation by clicking "setup". Then, after clicking "go", the turtles start moving and producing in the way explained above; they keep on doing so until the "go" button remains pressed.

Buttons: setup
resets everything to the random-beginning values and releases in the simulated economy a number of turtles which can be chosen by the "number of turtles" slider.

Buttons: go
if clicked, the model starts running.

Sliders: turtles-number
on the left of the screen, this slider allows you to choose the number of turtles you'd like to start the simulation with.

Sliders: debts-available
this slider allows you to change the amount of debts available in the bank.

Sliders: loan-limit
this slider allows you to change the wealth's treshold necessary to have access to the loan market.
  
Monitors:
on the left of the screen, below the start and go buttons, there are three monitors which indicate the total amount of debts granted by the bank, the total number of diamonds produced and the number of repayments.

Plot: Production
this plot monitors the number of diamonds producers.

Plot: Populations
this plot indicates the trend of the number of employed turtles compared to the number of poor turtles.

THINGS TO NOTICE
----------------
When the setup and go button are clicked, the turtles immediatly start to do economic transactions: some of them obtain a loan and then buy raw materials and hire workers, some others buy diamonds and so on.
After running the model for a few cycles, you see how a micro-credit institution can improve the general wealth level of a poor society. In particular, the number of poor turtles immediatly decreases, meanwhile the number of workers, producers and diamond buyers increases.  


THINGS TO TRY
-------------
Try different values of "microcredit-available". How does the model change if the amount of loans available for the turtles increases?

Move the slider of "turtles-number". How does this variation affect the results of the model?

Try different values of "loan-limit". Which are the effects on the model if you decrease the threshold necessary to obtain a loan?


EXTENDING THE MODEL
-------------------
This model simplifies the necessary procedures the turtles have to pursue to obtain the loan. Since microcredit, in the real world, is usually based on the constitution of a group of borrowers, one extension to the model could be to create this kind of groups where loans can be received in a continuous sequence.
In our simulation every borrower is warrantor of himself, while in the reality it is the whole group of borrowers that guarantees for every loan.

In our model, we hypothesize that the bank grants its loans at an interest rate equal to zero. The presence of an interest rate, applied by the bank on its loans, could therefore represent another possible extension.

Our model shows a close economy where only one bank exists and turtles can trade only among themselves; that means that after some cycles no more diamonds can be produced because of the endogenous lack of money. 
The model could be improved by opening the economy to foreign investments and trades, giving the possibility to the economy to continue in the direction of growth.

A further improvement could be to add the role of the information in the model, so that the turtles could become entrepreneur because of the informations they receive from the turtles that already are producers. 


CREDITS AND REFERENCES
----------------------
Hoekstra, R.(2005). Economicexchange. http://ccl.northwestern.edu/netlogo/models/community/economicexchange
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NetLogo 3.0
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