1. CS 121 Engineering Computation Lab Lab 3 Department of Computer Science Drexel University Summer 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.

2. Your class instructor and TA Instructor for this section: Office: Email: Your TAs are:

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

4. Lab 3 Overview Part 1 Scripts (ch. 4 readings)‏ Assignments (function)‏ Part 2 User defined functions

5. Assignments Assignments are of the form name := expression where a is a variable and n can be an expression (discussed in lab 2)‏ Name can be a single letter (upper-/lower- case sensitive), or a combination of a letter followed by letters and numbers and underscores. Aaa1exprI eqn1my_grade largestScore Some names are reserved by Maple and cannot be used as something to assign to: Pi for I end quit

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

7. Scripts What is a script? –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.

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?”)‏

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

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

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

12. Usage of User Defined Functions Format:function name (values for inputs)‏ Example: f := (x) -> sqrt(x) + 1 f(9) evaluates to 4 as a result. Example: g := (a, b) -> (a+b)/2 g(3.5, 6.5) evaluates to 5 as a result.

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);

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

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.

16. 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. Email 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. 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. Week 3 Take Quiz 3 Tuesday-Friday Week 3 –Maple TA server down for maintenance 9- 10am and briefly at 3pm each day during the week.

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