Eng. 6002 Ship Structures 1

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Eng. 6002 Ship Structures 1

• Introduction to Matlab

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What is Matlab?
Matlab is a commercial "Matrix Laboratory"
package which operates as an
interactive programming environment. Matlab is
available for PC's, Macintosh and UNIX
systems. Matlab is well adapted to numerical
experiments. Matlab program and script files
(m-files) always have filenames ending with ".m"
The programming language is
exceptionally straightforward since almost
every data object is assumed to be an
array. Graphical output (figure) is
available to supplement numerical results.
Online help is available from the Matlab prompt
(a double arrow) by typing help.
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What kind of graphics are possible in Matlab?
Polar plot t0.012pi
polar(t,abs(sin(2t).cos(2t)))
Line plot x00.055,ysin(x.2),plot(x,y)
Stem plot x 00.14, y
sin(x.2).exp(-x) stem(x,y)
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What kind of graphics is possible in Matlab?
Surface plot zpeaks(25), surf(z),
colormap(jet)
Mesh plot zpeaks(25), mesh(z)
Contour plot
zpeaks(25),contour(z,16)
Quiver plot
28 January 2003, Matlab tutorial Joanna Waniek
(jowa_at_soc.soton.ac.uk)
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Using Help in Matlab
Online help is available from the Matlab prompt
(gtgt a double arrow), both generally (listing of
all available commands) gtgt help a long list
of help topics follows and for specific
commands gtgt help fft a help message on the
fft function follows.
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What is Matlab?

• MATLAB consists of
• The MATLAB language
• a high-level matrix/array language with control
  flow statements, functions, data structures,
  input/output, and object-oriented programming
  features.
• The MATLAB working environment
• the set of tools and facilities that you work
  with as the MATLAB user or programmer, including
  tools for developing, managing, debugging, and
  profiling
• Handle Graphics
• the MATLAB graphics system. It includes
  high-level commands for two-dimensional and
  three-dimensional data visualization, image
  processing, animation, and presentation graphics.
• (contd)

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What is Matlab?

• The MATLAB function library.
• a vast collection of computational algorithms
  ranging from elementary functions like sum, sine,
  cosine, and complex arithmetic, to more
  sophisticated functions like matrix inverse,
  matrix eigenvalues, Bessel functions, and fast
  Fourier transforms as well as special image
  processing related functions
• The MATLAB Application Program Interface (API)
• a library that allows you to write C and Fortran
  programs that interact with MATLAB. It include
  facilities for calling routines from MATLAB
  (dynamic linking), calling MATLAB as a
  computational engine, and for reading and writing
  MAT-files.

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What is Matlab?

• Some facts for a first impression
• Everything in MATLAB is a matrix !
• MATLAB is an interpreted language, no
  compilation needed (but possible)
• MATLAB does not need any variable declarations,
  no dimension statements, has no packaging, no
  storage allocation, no pointers
• Programs can be run step by step, with full
  access to all variables, functions etc.

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What does matlab code look like?

• t 0pi/1002pi
• y sin(t)
• plot(t,y)

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What does matlab code look like?

• t 0pi/1002pi
• y sin(t)
• plot(t,y)

Remember EVERYTHING IN MATLAB IS A MATRIX !
creates 1 x 200 Matrix
Argument and result 1 x 200 Matrix
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• Rows and columns are always numbered starting at
  1
• A single number is really a 1 x 1 matrix in
  Matlab!
• Matlab variables are not given a type, and do
  not need to be declared
• Any matrix can be assigned to any variable

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Building matrices with A 2 7 4 A 2
7 4 A 2 7 4 3 8 9 B A A
2
7
4
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• A matrix can be indexed using another matrix, to
  produce a subset of its elements
• a 100 200 300 400 500 600 700 b 3 5
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• c a(b)
• 300 500 600

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Matrices

• a vector x 1 2 5 1
• x
• 1 2 5 1
• a matrix x 1 2 3 5 1 4 3 2 -1
• x
• 1 2 3
• 5 1 4
• 3 2 -1

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Matrices

• x(i,j) subscription
• whole row
• whole column

yx(2,3) y 4 yx(3,) y 3 2
-1 yx(,2) y 2 1 2
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Operators (arithmetic)

• addition
• - subtraction
• multiplication
• / division
• power
• complex conjugate transpose

. element-by-element mult ./ element-by-element
div . element-by-element power . transpose
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Operators (relational, logical)

• equal
• not equal
• lt less than
• lt less than or equal
• gt greater than
• gt greater than or equal
• AND
• OR
• NOT

• pi 3.14159265
• j imaginary unit,
• i same as j

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Generating Vectors from functions

• x zeros(1,3)
• x
• 0 0 0
• x ones(1,3)
• x
• 1 1 1
• x rand(1,3)
• x
• 0.9501 0.2311 0.6068

• zeros(M,N) MxN matrix of zeros
• ones(M,N) MxN matrix of ones
• rand(M,N) MxN matrix of uniformly distributed
  random numbers on (0,1)

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M-files

• Executing commands in the command window is fine
  for short scripts but when dealing with long
  scripts for complex problem-solving (or when
  programming) M-files is a must.
• It allows the user to write MATLAB command in a
  text file (called M-file) and then MATLAB will
  open the file and execute the commands exactly as
  it would if the user typed them at the MATLAB
  Command Window. The M-file editor is the MATLABs
  tool for creating M-files.

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m-files

• My first M-file
• x0pi/102pi
• fsin(x)
• gcos(x)
• plot(x,f,x,g,)
• xlabel(x')
• ylabel(y')
• title(sin(x) and cos(x))
• legend(sin(x),'cos(x))

We wish to write a MATLAB code (script) to plot
f(x) and g(x) on a single graph with labels,
title and legend. Where f(x) sin(x),g(x)
cos(x)
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Where is this going?

• As a final assignment in the course, we will be
  writing a Matlab script (or function) to solve a
  beam problem