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8/14/2019 Matlab Lecture 1w03
1/22
MATLAB - Lecture # 1
Topics Covered:
1. Introduction.
2. MATLAB windows.
3. Arithmetic operations with scalars.
4. Working in the command window.
5. Defining variables (scalars).
Starting with MATLAB / Chapter 1
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MATLAB is a software for numerical computations,
visualization and programming.The name MATLAB stands forMATrix LABoratory.
Its basic data element is an array (explained later).
With MATLAB you can:
Use it as a calculator.
Define variables and use them in calculations.
Use built-in functions (sin, cos,max,min, etc.).
Plot graphs.
Write and run computer programs.
Do symbolic calculations.
1-4
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Command Window: Main window that opens whenMATLAB is started. It has the command prompt .
All commands can be typed in this window. Used for
running programs written by user.
Figure Window: Contains graphs created by graphics
commands. This window opens automatically.
Editor Window: Used for writing and editing
programs. This window is opened from the File menuin the Command Window.
Help Window: Contains help information. This
window is opened from the Help menu in any of the
previous windows.
MATLAB windows:6
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Command Window(The Command Window opens
when MATLAB is started)
Command prompt
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Figure Window (The Figure Window opensautomatically by the plot command)
7
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(The Editor Window is opened from the
file menu in the Command Window)Editor Window
7
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Help Window (The Help Window can be opened from theHelp menu of any of MATLAB windows)
8
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WORKING IN THE COMMAND WINDOW
To type a command the cursor must be placed
after the command prompt (>>). Once a command is typed, and the Enter key is
pressed, the command is executed. (Only the last
command is executed. Everything executed before
is unchanged) It is not possible to go back to a previous line and
make a correction.
A previously typed command can be recalled tothe command prompt with the up-arrow key .( )
8-9
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ARITHMETIC OPERATIONS WITH SCALARS
NOTE: For scalars the arithmetic operations are the usual
ones. For vectors and matrices the arithmetic operations can
either follows matrix algebra rules, or can be performed on
element-by-element basis (discussed in the next lectures).
10
Operation Symbol Example
Addition + 5+3
Subtraction - 5-3
Multiplication * 5*3
Right Division / 5/3
Left Division \ 5\3=3/5
Exponentiation ^ 5^3
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ORDER Of PRECEDENCE
(The order in which operations are executed by the computer)
Higher-precedence operations are executed before lower-precedence operations.
If two operations have the same precedence, then the expression is
executed from left to right.
PRECEDENCE OPERATION
First Parentheses, starting with the innermost pair.
Second Exponentiation.
Third Multiplication and division (equal precedence).
Fourth Addition and subtraction (equal precedence).
10
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Using numbers:
8/2 is executed first
7+8 is executed first
5/3 is executed first
USING MATLAB AS A CALCULATOR
>> 7+8/2
ans =
11
>> (7+8)/2ans =
7.5000
>> 4+5/3+2
ans =
7.6667
Type and press Enter
Computer response
Type and press Enter
Computer response
Type and press Enter
Computer response
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5^3 is executed first,
/2 is executed next.
1/3 is executed first,
^ is executed next,
+ is executed last.
27^1 and 32^0.2 is
executed first,
/3 is executed next,+ is executed last.
5^3/2
ans =
62.5000>>
>> 27^(1/3)+32^0.2
ans =
5
>> 27^1/3+32^0.2
ans =
11
Type and press Enter
Computer response
Type and press Enter
Computer response
Type and press Enter
Computer response
11
12
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DISPLAY FORMATS
12-13
The format command controls how output numbers appear on the
screen. Input numbers can be written in any format.
format short (the default) 41.4286 Fixed-point with 4 decimal
digits.
format long 41.42857142857143 Fixed-point with 14 decimal
digits.
format short e 4.1429e+001 Scientific notation with 4
decimal digits.
format long e 4.142857142857143e+001 Scientific notation with
15 decimal digits.
Format bank 41.43 Two decimal digits.
MATLAB has several other formats in which numbers can be displayed.
13
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MATLAB BUILT-IN MATH FUNCTIONS
In addition to arithmetic operations, MATLAB can be used to
calculate elementary math functions. The most common ones are:
Examples:
>>
sin(0.78539)
ans =
0.7071
>> sqrt(169)
ans =
13
>> log10(10000)
ans =
4
MATLAB has hundreds of built-in functions (this will be discussed in
future lectures).
13-15
sin(x) x in radians
cos(x) x in radians
tan(x) x in radians
cot(x) x in radiansThe inverse is: asin(x),
acos(x), etc.
exp(x) exponential
log(x) natural logarithm
log10(x) base 10 logarithm
sqrt(x) square rootabs(x) absolute value
16
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THE ASSIGNMENT OPERATOR
Variable = A value, or a computable value
The left
hand side
can only beonevariable.
The right hand side can be a
specific value, or a computable
expression (an expression thatincludes values and/or previously
defined variables).
16-18
In MATLAB, the = sign is called the ASSIGNMENT
OPERATOR.
The ASSIGNMENT OPERATOR assigns a value to a variable.
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THE ASSIGNMENT OPERATOR
For example, if you type:
>> x = 3
x =
3
MATLAB assigns a new value to x, whichis the old value 3 plus 5.
(In mathematics this expression has no
meaning since it implies: 0 = 5.)
MATLAB assigns the value of 3 to x.
If then you type:
>> x = x +5
x =
8
For example, the statement:
x + 4 = 30 is not valid. MATLAB does not solve for x,
but the statement:
x = 30 4 is valid (the number 26 is assigned to x.)
16-18
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DEFINING VARIABLES
A variable is defined by typing a variable name followed by the
assignment operator (equal sign) and then a value, or a
mathematical expression.
Once a variable is defined, the computer remembers and stores its
value. The variable can then be used in further calculations.
>> a=8
a =
8
>> B=12
B =
12
>> a+B
ans =
20
>> a/B
ans =
0.6667
>> B/a
ans =
1.5000
>> B^a
ans =
429981696
Type and press Enter
Computer response
Type and press Enter
Computer response
16-18
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Variables can also be used to define new variables
Once in existence, variables can be used in functions
>> d=a*B
d =
96
>> sqrt(d)
ans =
9.7980
A previously defined variable can be redefined and reassigned
a new value.
16-18
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RULES ABOUT VARIABLES NAMES
Variable names can be up to 63 characters long.
Variable name can contain letters, digits, and
the underscore character.
Variable name must begin with a letter.
MATLAB is case sensitive; it distinguishes
between uppercase and lowercase letters. For
example,Aand a are not the same variable.
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PREDEFINED VARIABLES
>> pi
ans =
3.1416
Typing these variables gives:
>> eps
ans =
2.2204e-016
>> inf
ans =
Inf
>> i
ans =
0 + 1.0000i
>> sin(pi/4)
ans =
0.7071
18-19
MATLAB has several variables that are predefined.
These variables can be redefined to have any other value.It is probably better not to use the predefined variables as
variable names.
Some of the predefined variables are:
pi ( ), eps (the smallest difference between two numbers)
inf (infinity)
i (square root of 1) j (square root of 1)
ans (the value of the most recent calculation)
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