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Functions...

1. Refresh on old ones2. Refresh on the vocabulary3. Some new ones!

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1. Remember these functions?

clcclear

sin(), sind() …sqrt(), abs() …

input(), fprintf(), disp()

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2. Official vocabulary

variable = functions_name( argument list )

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.

2. MATLAB is “passing” inputs to the function.

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Various uses

• While the function’s name is ALWAYS needed, the call may/may not require either one of the other 2 parts.

variable = functions_name( argument list )

• For example…clc and clear require neithersind() requires 1 argument, and usually has a variable collecting the resultfprintf() requires at least 1 argument (the format string), but typically we do not collect the result.

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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 stringage = input(‘Enter your age: ’);

2 arguments: both stringsusername = input(‘Username: ’, ‘s’);

3 arguments: 1 string and 2 variablesfprintf(‘Hello %s! You are %d years old!\n’,…

username, age);

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Rounding functions

• Rounding floats to integer

*w.r.t = with respect to

Function Definitions Examples

2.453 12.56 -6.67

round() Rounds *w.r.t 0.5 __?__ 13 -7

ceil() Rounds towards +infinity 3 __?__ -6

floor() Rounds towards -infinity 2 12 __?__

+

-

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Examples

How many bags of concrete are needed to build stairs?

depthw

thick

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:

Civil Eng.

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Examples

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

Civil Eng.

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Example2 Hrs/Min/Sec

Convert 5632seconds to a format hrs:min:sec!

5632 secd = 1.56444444 hours3600 (secd/hr)

•Round down: 1 full hour

5623 sec – 1* 3600 sec = 2023 seconds

2023 secd = 33.71666 minutes60(secd/min)

•Round down: 33 full minutes

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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.

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Generating Random Numbers

• Generating random numbers

• rand() is another one of those versatile functionsx=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 matrixx=rand(2,5); %a 2-rows by 5-columns matrix

rand Generates one float between 0 and 1 both excluded.

rand(n) Generates a matrix with n^2 floats between 0 and 1 both excluded. (used in 2 weeks from now)

rand(n,m) Generates an n-row by m-column matrix with floats between 0 and 1 both excluded. (used in 2 weeks from now)

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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.

0 1

k

2 3

k

0 1

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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.

0 1

k

0 5

k

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End of algebra

• So.. Using a combination of arithmetic operators, how would you generate these values (both excluded):

k1 = rand_______________________;

k2 = rand_______________________;

15 20

k1

-5.5 5.5

k2

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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!

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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???

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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

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Wrapping up

• Vocabulary– Function call– Arguments– Collecting– Return-values– Versatile

• New notions– Rounding up/down/ or w.r.t 0.5– 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!!