Transcript PPT - Computer Science

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.
Your class instructor and TA
• Instructor for this section: Tim Cheeseman
Office: UC 147 (CLC)
Email: [email protected]
• Your TAs are:
061 – Cem Sahin, Lloyd Ricks
561 – Pat Lockner
Note that verification sheet requires you to put
down instructor’s name.
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
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.
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
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 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
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
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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:
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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.
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
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.
Weeks 5 and 6
• Take Quiz 3 Monday-Friday Week 6
– October 27-31
– Maple TA server down for maintenance 910am and briefly at 3pm each day during the
week.
– Greater penalty if you take the “late version”
of quiz.
Demo of RandomTools
Instructors can use the following slides optionally.
>
>
>
>
Demo of Import Data
Instructors can use the following slides optionally.
Demo of Import Data (cont’d)
Demo of Import Data (cont’d)
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