Introduction
，
Requirement
CSE 232, Lab Exercise 3
More Command Line
Pagers
Often, you want to be able to view files in the terminal (instead of opening them in a text
editor like Atom or gedit). There are a few ways view files from the terminal.
cat
The command cat is short for concatenate, which means to link things together.
The cat program is often used to link the output from one program to the input from
another. But another useful trait of cat is to output the contents of a file to the terminal.
Invoking the cat program is quite simple:
cat some_file_name.txt
The above command will print the contents of the file to the terminal. However, for large
files, cat is not very user-friendly. Instead, you should use a pager.
less
Pagers are programs that show you content one page at a time. They are useful for
viewing large files (files too big to fit in the terminal window). The most popular pager is
called less because it was derived from an older program called more , computer
science history is a little silly. You can invoke the less program like so:
less some_file_name.txt
To go the the next page, push the f key (forward). To go back a page, push the b key
(backwards). To quit the pager and return to the command line, push q (use your
imagination for why it is the q key).
Help
There are a few programs that are intended to provide documentation on the programs
install on your computer. However, they are often difficult to understand, especially for a
beginner. You invoke them by typing the help program and the name of the program you
want information about. They may open up a pager if the entry is long.
help
This command is used to provide information about tcsh , which is the language the
terminal in x2go is running (Mimir uses another called bash )
man
This command (short for manual) is used to retrieve the documentation about the
programs installed on the computer. They can be long (try man g++ for example. It
comes automatically with the pager keys described above).
You can search through large man files looking for a keyword. When the pager stops at
the bottom of the page you can type a /keyword. For example, if you type man g++ (a
big page), then you type /memory while the pager is active (command will show up in
the bottom of the window) it will page to the next example of the word memory in the
file. If you then hit the n key, it will go to the next example of memory in the file. You
can keep hitting n looking for the next example of a keyword. The q quits as before. If
you want to see more commands, hit the h key while the pager is active and it will give
you help in the pager.
info
This command is an alternate to man, often used by unix distributions.
Examples:
help cd
info ls
man python3
-h or –help
Many programs will give you a bit of documentation about themselves (like what
arguments they accept) if you invoke the program with the -h or –help flags. Example:
python –h
g++ –help
Assignment
Background
You remember calculus don’t you? The basic concept of an integral is the area under the
curve, the curve represented by some function. If you can integrate a function, you can
calculate that area directly, but for some functions it is easier to approximate that area
using discrete, iterative methods. We are going to investigate one of those methods, the
Trapezoid Rule () .
Trapezoid Rule, area of a Trapezoid
The basic idea is to draw a series of trapezoids that approximate the area under a curve,
where the more trapezoids we draw, the better the approximation.
First, remember how to calculate the area of a trapezoid?
One measures the length of the parallel sides (b 1 and b 2 ), then the distance between the
parallel sides (h) . Add the parallel distances, multiply those values by h, divide by 2.
Let’s rotate that trapezoid 90 o and model it as below. Now the b 1 length is the curve value
f(a), the b 2 length f(b) and the height h the difference between b – a.
f(a)%
f(b)%
a% b%
f(b)% f(a)%
b’a%
For two trapezoids next to each other with heights f(a), f(b) and f(c), f(b) a common side
used by the two trapezoids, we get the formula:
(b−a)[f(a)+ f(b)]
2
+
(c−b)[f(c)+ f(b)]
2
In general, for the definite integral:
1. from a to b
2. with n equally space trapezoids (n+1 points on the x axis)
3. grid spacing of h=(b-a/n)
Given the above, the area would be:
(b−a)* f(a)+ f(b) [ ]
2
Program Specifications
1. Write three functions:
a. a function fn to integrate over. Let’s use fn à −6x 2 +5x+3
i. fn takes a single double parameter, the value x
ii. fn returns a double, the result of the function evaluation
b. a function integral, the actual integral of fn which is integral à
−2x 3 +
5
2
x 2 +3x
i. integral takes a single double parameter, x
ii. integral returns a double, the result of the function
let’s further fix the interval to calculate the integral over as 0 to 1
c. a function trapezoid. The specification for trapezoid is:
i. take in three parameters:
1. the two definite points of the integral a and b as doubles
2. the number n, the number of trapezoids, a long
ii. calculates the area under the curve represented by the function fn
given the provided number of trapezoids over the interval 0 to 1.
iii. returns a double, the sum of the area of the trapezoids.
2. A main function that does the following:
a. takes in two values (in order)
i. a float value tolerance
ii. an initial guess at the number n, the number of trapezoids
b. you run a loop that measures the difference between the actual value of the
integration (you have the integral function so you can calculate the exact
value between a and b) and the estimated value from trapezoid
i. if the difference is within tolerance, report to the user 4, space
separated values on a single line. All output should be fixed,
setprecision(6)
1. n
2. estimate value
3. exact value
4. tolerance
ii. if the difference is not within tolerance, double the value of n and
rerun. Continue the doubling and re-running until the estimate of the
trapezoid function it is within tolerance of the actual value from
integral.
3. You can test this on Mimir, Lab03:calculus
Example Run
As I’ve said before, you might want to put some extra output in to check yourself before
you try the actual Mimir tests. This is what I did.