Download CS 121 Engineering Computation Lab - Computer Science

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.
Your class instructor and TA
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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 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.
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 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
• 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.
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 910am and briefly at 3pm each day during the
week.
Demo of RandomTools
Instructors can use the following slides optionally.
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