CS 121 Engineering Computation Lab Lab 3

Department of Computer ScienceDrexel 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.

Your class instructor and TA

• Instructor for this section:• Office:• Email:• Your TAs are:

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

Lab 3

• Overview

• Part 1 Scripts (ch. 4 readings)• Assignments (function)

• Part 2 User defined functions

Assignments

• Assignments are of the formname := 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.

A a a1 expr I eqn1 my_grade largestScore• Some names are reserved by Maple and cannot be used

as something to assign to:

Pi for I end quit

Demo of Assignments• p := x^2

x^2• p

x^2• p - 1=0

x ^ 2-1 = 0

• unassign(‘p’) • p

p• p-1=0

p-1=0• p does not stand for “x^2” any more.

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.

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?”)

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 forsheepEqn :=N = 220/(1+10*.83^t)popSize := 80

• Copy region• Edit

sheepEqn := N = 330/(1+10*.79^t);popSize := 85;

• Re-execute edited region

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

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

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.

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);

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

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.

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.

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.

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.

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Demo of RandomToolsInstructors can use the following slides optionally.