5/4/2009
1
Introduction
Ve 280
Programming and Introductory Data Structures
Ve 280 Manifesto
y
Mathematics
, especially as used by physics, is the formalism
we use to describe “what is”
y
The physical world is modeled by equations.
y
Solutions to these equations give us insight into the world.
y
Classical mathematics however does not say anything about how
Classical mathematics, however, does not say anything about how
these processes unfold.
For that, we need something else…
y
Computer Science
is the formalism we use to describe “how to”
y
The computer science world uses algorithms to do this.
y
Algorithm
:
An abstract sequence of actions composed to solve a
problem.
y
Program
:
A concrete set of
program statements
which
implement
some algorithm.
The Task of Programming
y
Accept a possibly incomplete and/or imprecise specification
of the problem.
y
Design
an
effective
algorithm that:
y
Correctly satisfies the specification.
y
Is efficient in its (asymptotic) usage of
space
and
time
(i.e.
how does it behave when we change problem parameters).
y
Implement
the algorithm
correctly
and
efficiently
y
An implementation of an algorithm is correct if it behaves as the
algorithm is intended for all inputs and in all situations.
Correctness is never negotiable.
The Task of Programming
(Implementation Cont’d)
y
There are three notions of an
efficient
implementation
y
The implementation has (concrete) space/time requirements
asymptotically similar to the more abstract requirements of the
corresponding algorithm.
y
Of ll f th "
t ti
ll
d"
ibl
i
l
t ti
Of all of the "asymptotically good" possible implementations,
this one is among the better ones in absolute, concrete terms.
y
It does not take an undue amount of effort for a programmer to:
y
Write the implementation in the first place (simplicity).
y
Improve/adapt the implementation to more general or closely related
algorithms (elegance).
y
So,
efficient
can mean fast, simple, and/or elegant.
The Task of Programming
y
Two more pieces of the programming puzzle:
y
Testing
y
Maintenance
y
These are often be overlooked when a deadline approaches.
However, they are very important and are covered in greater
detail in later courses.
The Task of Programming
y
This doesn’t seem too difficult, right?
y
What's the big deal?
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Programming Challenges
Conflicting goals
y
Engineering Goals:
Faster
,
Better
,
Cheaper
(
pick two
)
y
Unfortunately, our goals are often in conflict.
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 Summer '09
 Jeff
 Computer Science, Computer Programming, Data Structures, Programming Challenges, smaller marginal benefit

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