Videos
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 Boone,Ed,2010, Introduction to Functions in R
    (v35k,s5.7k,t6:29)
    https://www.youtube.com/watch?v=gl9opYcRxO8

 LearnR, 2014,  R Tutorial 35: Writing functions
    (v24k,s28k,t4:44)
    https://www.youtube.com/watch?v=-CTXR8qxTUI
 
 Tutorials Point (India) Pvt. Ltd., 2018, R programming -Functions
    (v5k,s980k,t3:00)
    https://www.youtube.com/watch?v=Vl9gSqi71Cs
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postman
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 Step 1: launch postman
 Step 2: Click "collections" on the left -> + [create new correction]
         e.g., myfirstTest
 Step 3: click three dots -> choose [Add request]
 step 4: Get
         https://simple-books-api.glitch.me
 Step 4B: https://simple-books-api.glitch.me/books
[
    {
        "id": 1,
        "name": "The Russian",
        "type": "fiction",
        "available": true
    },
    {
        "id": 2,
        "name": "Just as I Am",
        "type": "non-fiction",
        "available": false
    },
     [more]

 Step 4C: https://simple-books-api.glitch.me/books/:bookid
          endter 3 for bookid row
  {
    "id": 3,
    "name": "The Vanishing Half",
    "author": "Brit Bennett",
    "type": "fiction",
    "price": 16.2,
    "current-stock": 987,
    "available": true
   }
 Step 5: Params ->User type ->
         https://simple-books-api.glitch.me/books/:bookid?userType
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Retirement calculator 
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Source: http://money.cnn.com/calculator/retirement/retirement-need/

Step 1: estimate John Doe s final annual salary when he retires
	Input variables: 
         a) current salary
         b) salary growth rate (factor in the inflation rate)
         c) number of years before his retirement 

        For example, if John is 35 year-old and earning $50,000 now. If he plans 
            to retire at 67, his final annual salary will be 50000*(1+g)(67-35), 
            where g is the annual salary growth rate. 

Step 2: Estimate the required annual cash inflow for the first retirement year.
        For example, we could assume that the expected cash inflow for the 
        first year after retirement is 80% or 85% of his/her last annual salary. 

Step 3: estimate how many years after a person s retirement.  
        For instance, this value is 25 if John s life expectancy is 92 and retries at 67 (92-67). 

Step 4: estimate the present value, at the time he retires, of a growing annuity
	Input values: the 1st cash flow, a growth rate and an appropriate discount rate

Step 5: Factor in the social security benefit (this could be another data case)
	Estimate the present value, at time of your retirement, of your Social Security benefit
	Input values:
	Monthly benefit
	Discount rate

Step 6: John s net required cumulative wealth when he retires 
        (the result of Step 4 minus the result of Step 5)

Step 7: estimate John s required saving from now to that year. 
	Such as the annual saving or percentage saving

Primary Insurance Amount
    https://www.ssa.gov/oact/COLA/piaformula.html

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