1. CS 121 Engineering Computation Lab Lab 3
Department of Computer Science
Drexel University
February 2-6, 2009
©By the author. All rights reserved. Permission is given to CS121 Fall 2008 staff and students to use and reproduce these notes for their own use. 1 1 1

2. Your class instructor and TA
Instructor for this section: Tim Cheeseman Office: UC 147 (CLC)
Your TAs are: 061 – Cem Sahin, Lloyd Ricks 561 – Pat Lockner
Note that verification sheet requires you to put down instructor’s name. 2 2 2

3. Week 3 and 4 retrospective
Lab 2: fourth week
Limited Precision Arithmetic
Data structure, functions
Quiz 2: fourth week
Getting stuck on problems during the quizzes?
Use the Cyber Learning Center (UC147)‏
Use the discussion board for short questions 3 3 3

4. Lab 3 Overview Part 1 Scripts (ch. 4 readings)‏
Assignments (function)‏
Part 2 User defined functions
Part 3 Lists, sets and sequences
Operations
Random Number generation
Reading in data from an external file. 4 4 4

5. Assignments Assignments are of the form name := expression
where a is a variable and n can be an expression
Name can be a single letter (upper-/lower- case sensitive), or a combination of a letter followed by letters and numbers and underscores. A a a1 expr L eqn1 my_grade largestScore
Some names are reserved by Maple and cannot be used as something to assign to: Pi for I end quit 5 5 5

6. Demo of Assignments p := x^2 x^2 p p - 1=0 x ^ 2-1 = 0 unassign(‘p’)
p does not stand for “x^2” any more. 6 6 6 6

7. Scripts What is a script? How are scripts useful?
A script is a sequence of operations. Usually, the later operations use the results of the earlier ones.
Labels or assignments are used to make the references convenient.
How are scripts useful?
Scripts are useful when you expect to solve a series of similar problems.
Reuse: cut, paste, edit, re-execute. 7 7 7

8. Pointers on Script Use
Rather than use the clickable interface, it's better to lay out the operations textually one line at a time.
You can create a script using only clickable operations if you don't need to change the operations that are specified by pop-up menu.
Use assignments and labels to refer to results of previous steps.
Place "editable quantities" as assignments at the beginning of the script, rather than scattering the editing task all over the script ("I forget, what do I need to change?") 8 8 8

9. Demo of Script Use
Demo the sheep problem. Compared to the script given in section 4.5, we’re replacing the clickable operations with the function version of the solve, eval, and plot operations.
This solves the problem for sheepEqn :=N = 220/(1+10*.83^t) popSize := 80
Copy region
Edit sheepEqn := N = 330/(1+10*.79^t); popSize := 85;
Re-execute edited region 9 9 9

10. User Defined Functions
Maple users can define new functions
That is one of the key features that makes Maple less like a calculator and more like a programming language 10 10 10

11. How to define your own function
Through the clickable interface
The general form is from the f:=a->y in the Expression palette
User-defined function textually
function name:= input name-> expression involving inputs
The ( ....) - > .....defines the function.
The function name := gives the function a name 11 11 11

12. Usage of User Defined Functions
Format: function name (values for inputs)‏
Example: f := (x) -> sqrt(x) f(9) evaluates to 4 as a result.
Example: g := (a, b) -> (a+b)/ g(3.5, 6.5) evaluates to 5 as a result. 12 12 12

13. Demo of User Defined Functions
Define three functions t, s and p
t := n -> 1/n*sin(n*Pi*x);
s(m) = the sum of t(i)
s := m -> sum(t(2^i), i=1..m);
p(m) = produces a plot of s(m) for x between 0 and 4
p := m -> plot(s(m), x=0..4)
Here is one example of its use:
p(1); 13 13 13

14. Demo of sequences, lists, sets
Maple demo of:
Assignment
Use of indexing to get at pieces
Concatenation of sequences
Sequences as "inside" of function invocation: binomial(3,5); versus s := 1,2; binomial(s);
Convert sequence to list: [s]
Convert sequence to set: {s}
Convert list to sequence: op(L)
Convert set to sequence: op(S)
nops(...) gives number of elements
sort(list) sorts in ascending order; sort(list, `>`) descending 14 14 14

15. Script test data in Problem 1.2
Problem 1.2 asks you to generate a list of random numbers to test your scripts on. Just follow the directions, entering the instructions as listed. You should see a list of random numbers which you can apply your script to.
Don't worry about the random number generator's operating principles yet. This lab, we just want you to use the generator. 15 15 15

16. Script Data for Problem 3.1
Detailed procedures are in the lab direction
Importing
GradeData1 and GradeData2
Where are the two files?
Course website -> lab materials
Bb Vista -> Lab Exercises -> Import Data 16

17. Finishing up – save your work
Save worksheets onto the Desktop. You can call them Lab3Part1, Lab3Part2, etc. Or you could put all the work into one worksheet and just call it Lab 3.
Submit a copy to Blackboard site as evidence that you did the lab.
a copy to yourself and/or your lab partners as an attachment so you can look at what you did for review purposes later.
We will use this week's work in the next Lab. 17 17 17

18. Turn in your verification sheet
Make sure your name/user id/section number/ date,time/instructor name are on the verification sheet.
Get the verification sheet signed for all parts you completed and hand it in. 18 18 18

19. Weeks 5 and 6 Take Quiz 3 Monday-Friday Week 6 October 27-31
Maple TA server down for maintenance 9- 10am and briefly at 3pm each day during the week.
Greater penalty if you take the “late version” of quiz. 19 19 19

20. Demo of RandomTools Instructors can use the following slides optionally.
>
> 20

21. Demo of Import Data Instructors can use the following slides optionally.21

22. Demo of Import Data (cont’d)‏22

23. Demo of Import Data (cont’d)‏23

24. Demo of Import Data (cont’d)‏
Right Click on the Blue Matrix. Click Assign to a name.
The name used here is ‘thelist’
Convert the matrix to a list using
Mainlist := convert(thelist,list)‏
Perform the required operations on the list 24