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Functions...

Functions. Refresh on old ones Refresh on the vocabulary Some new ones!. 1. Remember these functions ?. clc clear sin(), sind () … sqrt (), abs() … input(), fprintf(), disp (). 2. Official vocabulary. variable = functions_name ( argument list ).

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Functions...

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  1. Functions... Refresh on old ones Refresh on the vocabulary Some new ones!

  2. 1. Remember these functions? clc clear sin(), sind() … sqrt(), abs() … input(), fprintf(), disp()

  3. 2. Official vocabulary variable = functions_name( argument list ) 2. MATLAB is “passing” inputs to the function. 1. This is a “function call”. MATLAB “calls upon the execution” of the code behind the keyword. 3. MATLAB “collects” the “return-value” inside this variable.

  4. Various uses • While the function’s name is ALWAYSneeded, the call may/may not require either one of the other 2 parts. variable = functions_name( argument list ) • For example… clc and clear require neither sind() requires 1 argument, and usually has a variable collecting the result fprintf() requires at least 1 argument (the format string), but typically we do not collect the result.

  5. Arguments? Collecting return values? • 1 or many arguments: • Some keywords are versatile in how many arguments they need • When there is a list of arguments, separate each with a comma: , 1 argument: a string age = input(‘Enter your age: ’); 2 arguments: both strings username = input(‘Username: ’, ‘s’); 3 arguments: 1 string and 2 variables fprintf(‘Hello %s! You are %d years old!\n’,… username, age); 

  6. Rounding functions • Rounding floats to integer *w.r.t = with respect to + -

  7. Examples Civil Eng. How many bags of concrete are needed to build stairs? • Step1: • - Assume there is a support system underneath. Only the steps need to be built. • Assume units are inches for the thickness and depth, and feet for the width • Each 80lbs bag allows for a coverage of 0.6 sq.ft over a 2inch thickness (so 2/12*.6 ft^3) • Step2: thick depth w

  8. Examples Civil Eng. How many bags of concrete are needed to build stairs? Step3: Assuming 4 stairs: 3ft wide, 7in tall, 11in deep totVolume(ft3) = Nb_stairs * width * depth * thick = 4 * 3* 7/12 * 11/12 = 6.42 ft^3 Number of bags = totVolume(ft3)/ volume1bag = 6.42/ (2/12*.6) = 64.166 bags

  9. Example2 Hrs/Min/Sec • Convert 5632seconds to a format hrs:min:sec! • 5632 secd = 1.56444444 hours • 3600 (secd/hr) • Round down: 1 full hour • 5623 sec – 1* 3600 sec = 2023 seconds • 2023 secd = 33.71666 minutes • 60(secd/min) • Round down: 33 full minutes

  10. Example2 Hrs/Min/Sec 2023 – 33*60 = 43 seconds Conclusion: 5632seconds is also: 01:33:43 The function used to round down is: ________ Best practice: go code this mini-example. Allow the user to enter the initial number of seconds.

  11. Generating Random Numbers • Generating random numbers • rand() is another one of those versatile functions x=rand; x=rand(); %some keep the () to remind themselves it is a function-call vs. a variable name. x=rand(1); %avoid, it’s overdoing it… x=rand(2); %a 2-rows by 2-columns matrix x=rand(2,5); %a 2-rows by 5-columns matrix 

  12. rand() and a little bit of algebra: +- • What happens to a number k between 0 and 1 if it is added to another number? For example: What can we say about: 2+k ? What can we say about: k-4 ? >> The interval shifts left/right. k 1 0 k 0 2 1 3

  13. rand() and a little bit of algebra: */ • What happens to a number k between 0 and 1 if it is multiplied by another number? For example: What can we say about: 5*k ? What can we say about: k/2 ? >> The interval grows/shrinks. k 0 1 k 0 5

  14. End of algebra • So.. Using a combination of arithmetic operators, how would you generate these values (both excluded): k1 = rand_______________________; k2 = rand_______________________; k1 k2 15 -5.5 20 5.5

  15. Conclusion • To generate 1 float in the interval : ]a,b[ k = rand*(b-a)+a; This is not a formula worth remembering.. Just remember algebra!

  16. Example1 Thermometer A new thermometer is being built. In addition to showing the temperature, the manufacturer also wants to indicate a warning if the temperature is above or equal to 104 degrees Fahrenheit. You are being paid ($$$) to develop the program that will eventually be within the thermometer. It’s been a year, and still no thermometer.. How long are you going to wait???

  17. Example2 Rockets 0/1’s? • How about rockets??? How does software get written? Do we waste a rocket each time? • During launch, so many sensors give back information!!! • A couple of them are…. • Doors locked? True/False • Oxygen flowing properly? True/False • Fuel being delivered to engine? True/False

  18. Wrapping up • Vocabulary • Function call • Arguments • Collecting • Return-values • Versatile • New notions • Rounding up/down/ or w.r.t0.5 • Generating random numbers • Generating 1 random float value • Manipulating it to desire random range wanted • Generating a zero/one to simulate false/true • Examples • Cement for stairs: ceil() • Time formatting: floor() • Temperature: rand() • Rocket: all of the above!!

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