Functions 1 parameter, 2 return-values

1. Functions1 parameter, 2 return-values "Conversion of time format" One problem. 5 steps to solve it.

2. Convert Time. Step1. • Problem: Given a time as a whole amount of seconds, convert it to hr:min:sc format using the method shown hereafter.

3. Convert Time. Step2. myTime = 32512 seconds • To calculate the hours, divide by 3600 (seconds/hr) • Find the minutes by converting the 0.0311 (hr) to minutes: • Find the seconds by converting the 0.8667 (min) to seconds: 32512 (sec) = 9.0311 (hr) = 9 full hr 3600 (sec/hr) 0.0311 (hr) * 60 (min/hr) = 1.8667 (min) = 1 full minute 0.8667(min) * 60 (sec/min) = 52 (sec)

4. Convert Time. Step3. hrs Keyboard ** MAGIC ** Screen Full time min sc

5. Convert Time. Step 4a. • Algorithm %prompt user for number of full seconds %divide by 3600 to get the hours %separate whole part and decimal part %multiply the decimal part by 60 to get the minutes %separate whole part and decimal part %multiply that decimal part by 60 to get the seconds %display result Code doing the same operation twice, on a different number, but SAME CODE. Let's create a function!

6. Overall Flow separate() CALL it once to solve for the minutes. Main script file CALL it once to solve for the seconds.

7. I/O of the function • One parameter, 2 return-values One value separate() The whole part The decimal part

8. Step.4b. Function Definition • Open a new script file, and type the following: The keyword function tells Matlab this is a function definition.

9. Function Definition When more than one return value are present, they MUST be in square brackets. Important: MATLAB does not return a vector with 2 values. This is just how MATLAB wants us to indicate multiple return values. It does return 2 separate values.

10. Function Definition The parameter goes on the right, in between ()

11. Function Definition The documentation shows how to use the function, what it does, and any assumptions made.

12. Saving the function definition SAVE THE FUNCTION. MATLAB offers automatically the correct name, i.e. the name of the function itself. Confirm by clicking Save.

13. Function Definition What would be the code if this was before you learned what a function was? Suppose: value = 2.45 whole = ? decimal = ?

14. Function Definition

15. Function Definition 2.45 2 .45 2.45 - 2

16. Function Definition 2.45 2 .45

17. Function Definition 9.0311 ?? ?? Same code, different input. 

18. Function definition: done! • Function: done! • But before we call our boss and colleague engineers to put the main script file together, we need to test!

19. Step5. Testing. • Once again, jump to the Command Window to experiment: (Imagine you were calling a built-in function.. It works the same way as with any other keyword, except you created the keyword separate()) Two separate scalars, NO VECTOR, even if we use [ ].

20. Step5. Testing (MISTAKE) • Remember that MATLAB only stores 1 value by default, and uses the default variable name ans. • This is the same, whether it is a built-in or programmer defined function. MATLAB does get two values returned by the function, BUT there are no variables COLLECTING them. MATLBA uses the default ans for the first one, but ignores the second return-value since it does not have a 2nd default variable name…

21. Step5. Testing • Note you can also test the documentation!!! (and should) >> doc separate <enter>

22. Back to step4b. • Now that the function works, your boss/colleagues/you may put together the main script file.

23. Step.4b. Main File %prompt user for number of full seconds %divide by 3600 to get the hours %separate whole part and decimal part %multiply the decimal part by 60 to get the minutes %separate whole part and decimal part %multiply that decimal part by 60 to get the seconds %display result Time to create the main script, and actually solve our conversion problem. REMEMBER: keep the main script file and the function definition in the same folder.

24. Write the FUNCTION CALLS. These lines "call upon the execution" of the code inside the definition, with various inputs each time. 1st call 2nd call

25. The 1st call converts the hrs whole = floor(value); decimal = value-whole;

26. The 2nd call converts the min • Same function: different ARGUMENT whole = floor(value); decimal = value-whole;

27. Step5. Testing • F5 yields: • 5.200000e+001 is the scientific notation for 52. • Due to round off issues, the final number of seconds has round off issues. •  Call the client to figure out how s/he wants this handled!

28. Use the function in another project! • BankOfAmerica ® has a program called "keep the change". • When a transaction is made on the debit card, the amount is rounded up to the nearest whole amount. The difference is automatically deposited in a savings account. • For example: transaction = $4.65. • $5 is debited from the checking account • $1 - $0.65 = $0.35 is credited to the savings account • Create a main script file that uses separate()to solve and indicate how much is placed in the savings account.

29. Wrapping Up • Please make sure you typed this example as we went along. • Returning two or more return-values makes us use [ ]. Do not use [ ] when there is only 1 value returned. It clutters the screen, and has no advantage. • MATLAB does not return an array, it is just the notation that requires the symbols. • CAUTION: the order of the variables matter. • Be courageous not to name all the variables the same everywhere. • Parameters are the variables inside the parentheses IN the function definition. • Arguments are the variables inside the parentheses IN the function call statement.