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Lecture 4: Input and output
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To print a variable in your display on the command window, its place must be indicted by % in the format-string followed by the format of presentation (d, f, e, g).
%d: integer notation
%f: fixed point (decimal) notation
%e: exponential notation
%g: whichever is shorter, %f or %e
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Nội dung Text: Lecture 4: Input and output
- Lecture 4
Input and Output
Input
input
fprintf
1
© 2007 Daniel Valentine. All rights reserved. Published by
Elsevier.
- Input
Input
Some options:
– Assign values to variables in a command line
Assign
using the equal ( = ) sign.
– Use the input function for interactive
Use
assignment of values to some of the variables
within your computer program.
within
2
- Input function
Input
General format:
variable = input('Please enter a value: ')
The display in the Command window:
Please enter a value:
Type a value after the displayed prompt;
Type
the variable now has been assigned the
value that was entered.
value
3
- Hands on
Area of a circle:
– Type this into an m-file:
radius = input('Please enter the radius: ')
radius input('Please
area = pi*radius^2
– Execute and see this display in Command Window:
Please enter the radius: 5.2
radius =
5.2000
5.2000
area =
84.9487
84.9487
4
- Hands on
Free falling object:
Type this into an m-file:
height_0=input('Please enter the initial height (in meters): ');
height_0=
time=input('Please enter the time the object was in the air (in seconds): ');
velocity_0=input('Please enter the initial velocity (in meters): ');
a=9.81;
height_f=height_0+velocity_0*time+(1/2)*a*time^2
Execute: See this display in Command Window:
Please enter the initial height (in meters): 25
Please enter the time the object was in the air (in seconds): 3
Please enter the initial velocity (in meters): 5
height_f =
84.1450
84.1450 5
- Input strings of text
Input
General format:
string = input('Please enter your name: ', 's')
string
The display in the Command window:
Please enter your name:
This is used when the input is a string
(e.g., names, months, etc.). The variable,
in this case, is a ‘char’ class (or type).
6
- Output options
The display variables:
– You can display the value of a variable in
You
different ways.
different
Typing “variable =” in the command window
x=500
x=
500
500
Using the fprintf command:
– Type into an m-file:
x=500;
fprintf('The value of x is %f.\n',x)
– Executing it displays in the Command Window:
The value of x is 500.
7
- fprintf()
fprintf()
The fprintf() command is one way to
The fprintf()
display the value of a variable with a label.
display
General format:
MATLAB code:
MATLAB
fprintf('format-string', variable)
fprintf('format-string',
Note: You can also use the disp() function to display
Note:
results. See the help on disp() and the examples in
the text.
the
8
- Placeholders in fprintf()
fprintf()
To print a variable in your display on the
To
command window, its place must be
indicted by % in the format-string followed
by the format of presentation (d, f, e, g).
by
%d: integer notation
integer
%f: fixed point (decimal) notation
fixed
%e: exponential notation
exponential
%g: whichever is shorter, %f or %e
9
- Hands on
Type into an m-file:
smiles=7
smiles=7
fprintf('Sarah smiles %d times a day.',smiles)
smiles day.',smiles
Executing it displays in the command window:
smiles =
7
Sarah smiles 7 times a day.
10
- Hands on
Type into an m-file:
month=input('Please enter your month of birth (i.e. May): ', 's');
month=
day=input('Please enter your number day of birth: ');
fprintf('Your birthday is %s %d!!',month,day)
Executing it displays in Command Window:
Please enter your number month of birth (i.e. May): August
Please enter your number day of birth: 11
Your birthday is August 11!!
11
- Format
When fprintf is used consecutively,
When fprintf
MATLAB prints the results on the same
line in the command window.
smiles=7;
smiles=7;
fprintf('Sarah smiles %d times a day.',smiles)
smiles day.',smiles
– After the second execution of this command:
Sarah smiles 7 times a day.Sarah smiles 7 times a day.>>
12
- The \n command
The \n
This command is a linefeed. It commands
MATLAB to start on a new line so that
sequential outputs are on separate lines.
– Example
waffles=4;
waffles=4;
fprintf('Erin ate %d waffles today.\n',waffles)
Erin ate 4 waffles today.
>>
– Be sure to use \n, not /n.
13
- Width & precision fields
Width
The width field
specifies the minimum
The width
number of characters to be printed.
number
The precision field specifies the number of
The precision
those characters that will show up after the
decimal point.
decimal
14
- Hands on
%8.2f specifies that there can be no less than 8
characters in the displayed output, and that two of
them are to follow the decimal point.
weight= 57638.75;
weight=
fprintf('The weight is %8.2f pounds \n', weight)
weight
fprintf(‘The weight is %50.2f pounds \n’, weight)
weight
The weight is 57638.75 pounds
The weight is 57638.75 pounds
– Notice the blank spaces in the second output.
– Use %% to have a % sign show up in output.
Use %%
15
- Summary I/O
Summary I/O
input
– variable = input('Please enter a value: ')
– string = input('Please enter a value: ', 's')
fprintf
– fprintf('formatstring', variable)
%f = fixed point (decimal) notation
–
%e = exponential notation
–
%g = whichever is shorter, %f or %e
–
16
- Lecture 5
MATLAB functions
Basics of Built-in Functions,
Basics
Help Feature,
Help
Elementary Functions (e.g., Polynomials,
Elementary
Trigonometric Functions),
Data Analysis, Random Numbers,
Complex Numbers
Complex
17
© 2007 Daniel Valentine. All rights reserved. Published by
Elsevier.
- What is a built-in function?
What
A computational expression that uses one or
computational
more input values to produce an output value.
more
MATLAB Functions have 3 components:
input, output, and name
output name
b = tan(x)
tan(
x is the input, b is the output, and tan is the
input output and tan
name of a built-in function; iin this case, it is the
n
name
tangent function with argument in radians.
tangent
18
- MATLAB functions
Functions take the form:
variable = function(number or variable)
variable
MATLAB has many functions stored in its file
MATLAB
system.
system.
To use one of the built-in functions, you need to
To
know its name and what the input values are.
know
For example, the square root function: sqrt().
For square
Find the square root of 9 using MATLAB
a = sqrt(9)
sqrt(9)
19
- HELP feature
HELP
You may not always recall the name and
You
syntax of a function you want to use since
MATLAB has so many built-in functions.
MATLAB
MATLAB has an indexed library of its built-
iin functions that you can access through
n
the help feature.
help
If you type help in the command window
If help
MATLAB provides a list of help topics.
MATLAB
20
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