Cash Flow

1 collaborator

Uri Wilensky (Author)

WHAT IS IT?

This model is a simple extension of the model "Bank Reserves". The purpose of the model is to help the user examine whether there is a relationship between the reserve ratio that banks must keep and the degree of equality in the distribution of the money that exist in the system.

It models the creation of money in an economy through a private banking system. As most of the money in the economy is kept in banks but only a little of it needs to be used (i.e. in cash form) at any one time, the banks need only keep a small portion of their savings on-hand for those transactions. This portion of the total savings is known as the banks' reserves. The banks are then able to loan out the rest of their savings. The government (the user in this case) sets a reserve ratio mandating how much of the banks' holdings must be kept in reserve at a given time. One 'super-bank' is used in this model to represent all banks in an economy. As this model demonstrates, the reserve ratio is the key determiner of how much money is created in the system.

HOW IT WORKS

In each round, people (represented by turtles) interact with each other to simulate everyday economic activity. Given a randomly selected number, when a person is on the same patch as someone else it will either give the person two or five dollars, or no money at all. After this, people must then sort out the balance of their wallet with the bank. People will put a positive wallet balance in savings, or pay off a negative balance from funds already in savings. If the savings account is empty and the wallet has a negative balance, a person will take out a loan from the bank if funds are available to borrow (if bank-to-loan > 0). Otherwise, the person maintains the negative balance until the next round. Lastly, if someone has money in savings and money borrowed from the bank, that person will pay off as much of the loan as possible using the savings.

The number of rich people in each moment is calculated by enumerating the number of people whose savings exceed 10 dollars. The number of poor people is the number of people whose loans exceed 10 dollars. The rest of the people are considered to belong to the "middle-class".

HOW TO USE IT

The RESERVES slider sets the banking reserve ratio (the percentage of money that a bank must keep in reserve at a given time). The PEOPLE slider sets the number of people that will be created in the model when the SETUP button is pressed. The SETUP button resets the model: it redistributes the patch colors, creates PEOPLE people and initializes all stored values. The GO button starts and stops the running of the model and the plotter.

THINGS TO NOTICE

There are numerous display windows in the interface to help the user see where money in the economy is concentrated at a given time. SAVINGS-TOTAL indicates the total amount of money currently being kept in savings (and thus, in the banking system). LOANS-TOTAL is the amount the bank has lent out. WALLETS-TOTAL gives an indication of the total amount of money kept in the peoples' wallets. This figure may be negative at times when the bank has no more money to loan (the turtle will maintain a negative wallet balance until a loan is possible). MONEY-TOTAL indicates the total-amount of money currently in the economy (SAVINGS-TOTAL + WALLETS-TOTAL). Because WALLETS-TOTAL is generally kept at 0 in this model (we are assuming that everyone deposits all they can in savings), MONEY-TOTAL and SAVINGS TOTAL tend to be the same.

The three lower monitors show the number of rich, middle-class, or poor people. A person's color tells us whether he is rich (green color), middle-class (gray), or poor (red).

There are four plots to help you observe the operation of the economy. Plot 1 plots the number of LOANS-TOTAL and MONEY-TOTAL as a function of time. Plot 2 plots the number of SAVINGS-TOTAL and WALLETS-TOTAL. Plot 3 plots income distribution and is the feature that you should pay the most attention to. The green pen plots the number of rich people; the black pen plots the number of middle-class people; the red pen plots the number of poor people. Finally, the fourth plot is a histogram that depicts how wealth is distributed among the population. Wealth is distributed in ten bars. Each bar corresponds to one tenth of the range of wealth. The gray line in the histogram represents the mean wealth value of all the turtles.

THINGS TO TRY

Vary the RESERVES rate as the model runs, and watch the effect this has on income distribution. You can either watch the three Income Distribution monitors, or the Income Distribution plot. Set RESERVES initially to 100 and observe the Income Distribution plot. Gradually lower RESERVES and see the effect on wealth distribution. Can you see whether the two of them are positively, negatively, or not related?

EXTENDING THE MODEL

Try extending the model to include payments of interest in the banking system. People with money deposited in savings should be credited with interest on their account (at a certain rate) from the bank from time to time. People with money on loan should make interest payments on their account to the bank from time to time.

This model has turtles interact in a very simple way to have money change hands (and create a need for loans). Try changing the model so that money moves around the system in a different way.

RELATED MODELS

Bank Reserves

HOW TO CITE

If you mention this model in a publication, we ask that you include these citations for the model itself and for the NetLogo software:

Wilensky, U. (1998). NetLogo Cash Flow model. http://ccl.northwestern.edu/netlogo/models/CashFlow. Center for Connected Learning and Computer-Based Modeling, Northwestern Institute on Complex Systems, Northwestern University, Evanston, IL.
Wilensky, U. (1999). NetLogo. http://ccl.northwestern.edu/netlogo/. Center for Connected Learning and Computer-Based Modeling, Northwestern Institute on Complex Systems, Northwestern University, Evanston, IL.

COPYRIGHT AND LICENSE

CC BY-NC-SA 3.0

This work is licensed under the Creative Commons Attribution-NonCommercial-ShareAlike 3.0 License. To view a copy of this license, visit http://creativecommons.org/licenses/by-nc-sa/3.0/ or send a letter to Creative Commons, 559 Nathan Abbott Way, Stanford, California 94305, USA.

Commercial licenses are also available. To inquire about commercial licenses, please contact Uri Wilensky at uri@northwestern.edu.

This model was created as part of the project: CONNECTED MATHEMATICS: MAKING SENSE OF COMPLEX PHENOMENA THROUGH BUILDING OBJECT-BASED PARALLEL MODELS (OBPML). The project gratefully acknowledges the support of the National Science Foundation (Applications of Advanced Technologies Program) -- grant numbers RED #9552950 and REC #9632612.

This model was converted to NetLogo as part of the projects: PARTICIPATORY SIMULATIONS: NETWORK-BASED DESIGN FOR SYSTEMS LEARNING IN CLASSROOMS and/or INTEGRATED SIMULATION AND MODELING ENVIRONMENT. The project gratefully acknowledges the support of the National Science Foundation (REPP & ROLE programs) -- grant numbers REC #9814682 and REC-0126227. Converted from StarLogoT to NetLogo, 2001.

Comments and Questions

Click to Run Model

globals [
  bank-loans
  bank-reserves
  bank-deposits
  bank-to-loan
  xmax
  ymax
  rich
  poor
  middle-class
  income-max
]

turtles-own [
  savings
  loans
  wallet
  temp-loan
  wealth
  customer
]

;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;;                     ;;;
;;;  Setup Procedures   ;;;
;;;                     ;;;
;;;;;;;;;;;;;;;;;;;;;;;;;;;

to setup
  clear-all
  initialize-settings
  crt people [setup-turtles]
  poll-class
  setup-bank
  set xmax 300
  set ymax (2 * money-total)
  reset-ticks
end 

to initialize-settings
  set rich 0
  set poor 0
  set middle-class 0
  set income-max 10
end 

to setup-turtles  ;;Turtle Procedure
  set shape "person"
  setxy random-xcor random-ycor
  set wallet (random 2 * income-max)
  set savings 0
  set loans 0
  set wealth 0
  set customer -1
  get-color
end 

to setup-bank
  set bank-loans 0
  set bank-reserves 0
  set bank-deposits 0
  set bank-to-loan 0
end 

;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;;                     ;;;
;;; Run Time Procedures ;;;
;;;                     ;;;
;;;;;;;;;;;;;;;;;;;;;;;;;;;

to go
  ask turtles [do-business]
  ask turtles [
    balance-books
    get-color
  ]
  bank-balance-sheet
  poll-class
  tick
end 

;; polls the number in each corresponding economic class

to poll-class
  set rich (count turtles with [savings > income-max])
  set poor (count turtles with [loans > income-max])
  set middle-class (count turtles) - (rich + poor)
end 

to do-business  ;;Turtle Procedure
  rt random 360
  fd 1
  ;; turtle has money to trade with, and there is
  ;; another turtle to trade with on the same patch
  if ((savings > 0) or (wallet > 0) or (bank-to-loan > 0)) [
    set customer one-of other turtles-here
    if customer != nobody and (random 2) = 0          ;;50% chance of trading
      [ifelse (random 2 = 0)                          ;;50% chance of trading $2 or $5, if trading
         [ask customer [set wallet wallet + 5]
          set wallet (wallet - 5)]
         [ask customer [set wallet wallet + 2]
          set wallet (wallet - 2)]
      ]
  ]
end 

;; Check the balance of our wallet.
;; Put a positive balance in savings.  Try to get a loan to cover a
;; negative balance.  If we cannot get a loan (if bank-to-loan < 0)
;; then maintain the negative wallet balance until the next round.

to balance-books  ;;Turtle Procedure
  ifelse (wallet < 0)
   [ifelse (savings >= (- wallet))
      [withdraw-from-savings (- wallet)]
      [if (savings > 0)
         [withdraw-from-savings savings]
       set temp-loan bank-to-loan
       ifelse (temp-loan >= (- wallet))
         [take-out-a-loan (- wallet)]
         [take-out-a-loan temp-loan]
      ]
   ]
   [deposit-to-savings wallet]

;; repay loans if savings are available
  if (loans > 0) and (savings > 0) [
    ifelse (savings >= loans)
      [withdraw-from-savings loans
       repay-a-loan loans]
      [withdraw-from-savings savings
       repay-a-loan wallet]
  ]
end 


;; Sets aside required amount from liabilities into
;; reserves, regardless of outstanding loans.  This may
;; result in a negative bank-to-loan amount, which
;; means that the bank will be unable to loan money
;; until it can set enough aside to account for reserves.

to bank-balance-sheet
  set bank-deposits sum [savings] of turtles
  set bank-loans sum [loans] of turtles
  set bank-reserves ((reserves / 100) * bank-deposits)
  set bank-to-loan (bank-deposits - (bank-reserves + bank-loans))
end 

to deposit-to-savings [amount]  ;; Turtle Procedure
  set wallet (wallet - amount)
  set savings (savings + amount)
end 

to withdraw-from-savings [amount]  ;; Turtle Procedure
  set wallet (wallet + amount)
  set savings (savings - amount)
end 

to repay-a-loan [amount]  ;; Turtle Procedure
  set loans (loans - amount)
  set wallet (wallet - amount)
  set bank-to-loan (bank-to-loan + amount)
end 

to take-out-a-loan [amount]  ;; Turtle Procedure
  set loans (loans + amount)
  set wallet (wallet + amount)
  set bank-to-loan (bank-to-loan - amount)
end 


;; color codes the rich (green),
;; middle-class (gray), and poor (red)

to get-color ;;Turtle Procedure
  set color gray
  if (savings > income-max) [set color green]
  if (loans > income-max)  [set color red]
  set wealth (savings - loans)
end 

to-report savings-total
  report sum [savings] of turtles
end 

to-report loans-total
  report sum [loans] of turtles
end 

to-report wallets-total
  report sum [wallet] of turtles
end 

to-report money-total
  report sum [wallet + savings] of turtles
end 


; Copyright 1998 Uri Wilensky.
; See Info tab for full copyright and license.

There are 10 versions of this model.

Uploaded by	When	Description	Download
Uri Wilensky	over 11 years ago	Updated to NetLogo 5.0.4	Download this version
Uri Wilensky	about 12 years ago	Updated version tag	Download this version
Uri Wilensky	about 12 years ago	Updated to version from NetLogo 5.0.3 distribution	Download this version
Uri Wilensky	almost 13 years ago	Updated to NetLogo 5.0	Download this version
Uri Wilensky	over 14 years ago	Updated from NetLogo 4.1	Download this version
Uri Wilensky	over 14 years ago	Updated from NetLogo 4.1	Download this version
Uri Wilensky	over 14 years ago	Updated from NetLogo 4.1	Download this version
Uri Wilensky	over 14 years ago	Updated from NetLogo 4.1	Download this version
Uri Wilensky	over 14 years ago	Model from NetLogo distribution	Download this version
Uri Wilensky	over 14 years ago	Cash Flow	Download this version

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Cash Flow.png	preview	Preview for 'Cash Flow'	over 11 years ago, by Uri Wilensky	Download

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