This chapter presents the following content: Matlab environment, built-in matlab functions, plotting, user-defined functions, numerical techniques, matlab environment, numerical techniques,...
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Nội dung Text: Lecture note Data visualization - Chapter 32
- Lecture 32
- Chapter 4 "Inheritance"
Inheritance is a powerful feature that allows the reuse of
code.
However, be sure that functions applied to objects created
at run time through the new operator are bound at run
time. This feature is known as dynamic binding, and the
use of virtual functions is required to ensure that runtime
decisions are made.
Reread this chapter as often as necessary to ensure that
you understand the distinctions among
nonvirtual functions
- Chapter 6 “Algorithm
Analysis"
In this chapter we introduced algorithm analysis and
showed that algorithmic decisions generally influence the
running time of a program much more than programming
tricks do
We also showed the huge difference between the running
times for quadratic and linear programs and illustrated that
cubic algorithms are, for the most part, unsatisfactory
We examined an algorithm that could be viewed as the
basis for our first data structure
The binary search efficiently supports static operations
thereby providing a logarithmic worstcase search
- Data Visualization with
MATLAB
Chapter 2 “MATLAB Environment”
Chapter 3 “Builtin MATLAB Functions”
Chapter 5 “Plotting”
Chapter 6 “UserDefined Functions”
Chapter 13 “Numerical Techniques”
- Chapter 2 "MATLAB
Environment"
In this chapter, we introduced the basic MATLAB
structure
The MATLAB environment includes multiple windows,
four of which are open in the default view:
Command window
Command history window
Workspace window
Current folder window
In addition, the
- Continued….
Variables defined in MATLAB follow common computer
naming conventions:
Names must start with a letter.
Letters, numbers, and the underscore are the only characters
allowed.
Names are case sensitive.
Names may be of any length, although only the first 63
characters are used by MATLAB
Some keywords are reserved by MATLAB and cannot be
used as variable names
MATLAB allows the user to reassign function names as
- Continued….
Matrices often store numeric information, although they
can store other kinds of information as well
Data can be entered into a matrix manually or can be
retrieved from stored data files
When entered manually, a matrix is enclosed in square
brackets, elements in a row are separated by either
commas or spaces, and a new row is indicated by a
semicolon:
a = [1 2 3 4; 5 6 7 8]
Evenly spaced matrices can be generated with the colon
- Continued….
MATLAB follows the standard algebraic order of
operations
MATLAB supports both standard (decimal) and scientific
notation
It also supports a number of different display options. No
matter how values are displayed, they are stored as
doubleprecision floatingpoint numbers
MATLAB variables can be saved or imported from
either .MAT or .DAT files
The .MAT format is proprietary to MATLAB and is used
because it stores data more efficiently than other file
- Chapter 3 “Builtin MATLAB
Functions"
General mathematical functions, such as
exponential functions
logarithmic functions
roots
Rounding functions
Functions used in discrete mathematics, such as
factoring functions
primenumber functions
Trigonometric functions, including
- Continued….
Data analysis functions, such as
maxima and minima
averages (mean and median)
sums and products
sorting
standard deviation and variance
Randomnumber generation for both
uniform distributions
Gaussian (normal) distributions
- Chapter 5 “Plotting"
The most commonly used graph in engineering is the x –
y plot
This twodimensional plot can be used to graph data or to
visualize mathematical functions
No matter what a graph represents, it should always
include a title and x and y axis labels
Axis labels should be descriptive and should include
units, such as ft/s or kJ/kg MATLAB includes extensive
options for controlling the appearance of your plots
The user can specify the color, line style, and marker style
for each line on a graph
- Continued….
In addition to x – y plots, MATLAB offers a variety of
plotting options, including polar plots, pie charts, bar
graphs, histograms, and x – y graphs with two y –axes
The scaling on x – y plots can be modified to produce
logarithmic plots on either or both x – and y axes
Engineers often use logarithmic scaling to represent data
as a straight line
The function fplot allows the user to plot a function
without defining a vector of x and y –values
MATLAB automatically chooses the appropriate number
- Continued….
The threedimensional plotting options in MATLAB
include a line plot, a number of surface plots, and contour
plots
Most of the options available in two dimensional plotting
also apply to these threedimensional plots
The meshgrid function is especially useful in creating
threedimensional surface plots
Interactive tools allow the user to modify existing plots
These tools are available from the figure menu bar
Plots can also be created with the interactive plotting
option from the workspace window
- Chapter 6 “User Defined
Functions"
MATLAB contains a wide variety of builtin functions
However, you will often find it useful to create your own
MATLAB functions
The most common type of userdefined MATLAB
function is the function Mfile, which must start with a
functiondefinition line that contains
the word function
a variable that defines the function output
a function name
a variable used for the input argument
- Continued….
The function name must also be the name of the Mfile in
which the function is stored
Function names follow the standard MATLAB naming
rules
Like the builtin functions, userdefined functions can
accept multiple inputs and can return multiple results
Comments immediately following the functiondefinition
line can be accessed from the command window with the
help command
Variables defined within a function are local to that
function. They are not stored in the workspace and cannot
- Continued….
Groups of userdefined functions, called “toolboxes,” may
be stored in a common directory and accessed by
modifying the MATLAB® search path. This is
accomplished interactively with the path tool, either from
the menu bar, as in
File > Set Path
or from the command line, with pathtool
MATLAB provides access to numerous toolboxes
developed at The MathWorks or by the user community
Another type of function is the anonymous function,
- Chapter 13 “Numerical
Techniques"
Tables of data are useful for summarizing technical
information
However, if a value is needed that is not included in the
table, must approximate that value by using some sort of
interpolation technique
MATLAB includes such a technique, called interp1 . This
function requires three inputs: a set of x values, a
corresponding set of y values, and a set of x values for
which you would like to estimate y values
The function defaults to a linear interpolation technique,
which assumes that approximate these intermediate y
- Continued….
A different linear function is found for each set of two
data points, ensuring that the line approximating the data
always passes through the tabulated points
The interp1 function can also model the data by using
higherorder approximations, the most common of which
is the cubic spline
The approximation technique is specified as a character
string in a fourth optional field of the interp1 function
If it’s not specified, the function defaults to linear
interpolation. An example of the syntax is
new_y = interp1(tabulated_x, tabulated_y, new_x, 'spline')
- Continued….
In addition to the interp1 function, MATLAB includes a
twodimensional interpolation function called interp2 , a
threedimensional interpolation function called interp3 ,
and a multidimensional interpolation function called
interpn
Curvefitting routines are similar to interpolation
techniques
However, instead of connecting data points, they look for
an equation that models the data as accurately as possible
Once you have an equation, you can calculate the
corresponding values of y
- Continued….
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