Basics of MATLAB and Beyond

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We define a red disc by setting all the pixels that are within a circle toone; all the other pixels are zero. The circle is defined by the equation:(x − x 0 ) 2 +(y − y 0 ) 2 = R 2 ,where (x 0 ,y 0 ) is the centre of the circle, and R is the radius. We set thecentre of the red disc to (−0.4, −0.4) and the radius to 1.0:R = 1.0;r = zeros(size(x));rind = find((x + 0.4).^2 + (y + 0.4).^2 < R^2);r(rind) = 1;The green and blue discs are defined in the same way, just shifting thecentre of the circle in each case:g = zeros(size(x));gind = find((x - 0.4).^2 + (y + 0.4).^2 < R^2);g(gind) = 1;b = zeros(size(x));bind = find(x.^2 + (y - 0.4).^2 < R^2);b(bind) = 1;Now we concatenate the matrices r, g, and b into one 200 × 200 × 3matrix called rgb:rgb = cat(3,r,g,b);We use rgb as an input to imagesc, which interprets the intensities inthe range 0.0 to 1.0:imagesc(rgb)axis equal offOn your screen you can see these as overlapped discs of coloured light.Exercise 13 Redefine the red, green, and blue discs so thatinstead of a circular disc of light at uniform maximum intensity,the intensity increases within each circle from zero at the centreto one at the edge; outside the circles the intensity should be zero.Create the new overlapped image. (Answer on page 189.)c○ 2000 by CRC Press LLC
An Application of RGB ImagesTo see how RGB images can be used, we look at how an image can befiltered. An image of the Cat’s Eye Nebula, which is stored on disk as aJPEG image, can be read into matlab using the imread command:>> q = imread(’ngc6543a.jpg’);>> size(q)ans =650 600 3The result is a 650×600×3 matrix, where the “pages” represent respectivered, green, and blue intensities. We can display the image by typing:image(q)axis image off(See page 120 for a description of axis image.) On your screen thisappears as a colour image. Suppose we want to filter out the red component.We do this by setting the first “page”, the red component ofthe image, equal to zero. First we take a copy of the original so we canlater plot the two images side by side:q_original = q;q(:,:,1) = 0;subplot(221)image(q_original)axis image offsubplot(222)image(q)axis image off29.4 Example: SonarLet us look at some sonar data consisting of sound spectral power levelsmeasured as a function of frequency, direction of arrival, and time. Loadthis data from the file sonar.mat:>> load sonarc○ 2000 by CRC Press LLC
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BASICS OFMATLAB®and Beyondc○ 200
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Library of Congress Cataloging-in-P
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typing pwd (print working directory
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ContentsIBasics of MATLAB1 First St
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20 Time-Frequency Analysis21 Line A
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39Answers to Exercises (Part I)40 A
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Set → Getting Started with MATLAB
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1.5 The Colon OperatorTo generate a
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matlab will recall the last command
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a = zeros(2,3)a =0 0 00 0 0>> b = o
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[a a(a)]ans =1 2 3 1 4 74 5 6 2 5 8
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a + bans =11 3344 6677 993.8 Transp
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4.2 Adding PlotsWhen you issue a pl
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x = [[1 2 3 4]’ [2 3 4 5]’ [3 4
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4.7 AxesSo far we have allowed matl
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v =1122>> v*uans =1 2 0 11 2 0 12 4
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max returns a vector containing the
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s = 100*spiral(3)s =700 800 900600
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We can plot the surface z as a func
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The contour function plots the cont
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m = gray(8);colormap(m)imagesc(1:10
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hold onplot3(x(ind),y(ind),z(ind),
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z = 5*ones(3,3)z =5 5 55 5 55 5 5>>
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contour(x,y,z,30);You may have noti
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variables that are local to themsel
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SwitchThe basic form of a switch st
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i =i =123136Vectorised Codematlab i
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9.1 MATLAB FormatTo save all the va
Page 58 and 59: 11 StartupEach time you start matla
Page 60 and 61: Where p i is the population for yea
Page 62 and 63: NaNs by leaving them off the plot.
Page 64 and 65: clfpolar(t,gdb)In this case you mus
Page 66 and 67: -0.5000-0.3750-0.2500-0.125000.1250
Page 68 and 69: the periodograms of the blocks, and
Page 70 and 71: plot(y(1:1000))axis([0 1000 -5 5])z
Page 72 and 73: comet(x,y)(You can get a three-dime
Page 74 and 75: By clicking within the panner box a
Page 76 and 77: x = linspace(-1,1,8192);Fs = 1000;y
Page 78 and 79: 23.3 Graphical Object Hierarchymatl
Page 80 and 81: Now we need to get the handles of a
Page 82 and 83: Beyond the BasicsPreludeThis part o
Page 84 and 85: clfgplot(A,[x y])axis off(Try zoomi
Page 86 and 87: str =you’re the one>> str = ’
Page 88 and 89: strrep(str,’go’,’am’)ans =I
Page 90 and 91: ans =3.14159e+100Some additional te
Page 92 and 93: eval(str)v =1 2 3 4 5The eval(str)
Page 94 and 95: Inline objects, like every other ma
Page 96 and 97: a(1,1) = {[1 2 3]}a =[1x3double]or>
Page 98 and 99: t = {’help’ spiral(3) ; eye(2)
Page 101 and 102: meteo.Temperatureans =24ans =19.000
Page 103 and 104: 3 >> a = [1 2 ;4 5 6;7 8 9]a =1 2 3
Page 105 and 106: [x,y] = meshgrid(1:5,1:3)x =1 2 3 4
Page 107: ans(:,:,2) =999And to sum over “p
Page 111 and 112: You can see that over the 8 time st
Page 113 and 114: name>> staff(2,1,2).name(5:9)ans =B
Page 115 and 116: q =7 8 96 1 25 4 3>> save saved_dat
Page 117 and 118: fid = fopen(’asc.dat’);The fope
Page 119 and 120: display and the enclosed area is th
Page 121 and 122: MarkerEdgeColor = auto(and so on)In
Page 123 and 124: text(-.7,f(-.7),’f(X)’)But we h
Page 125 and 126: plt(x,f(x/2),’--’)Let us try ca
Page 127 and 128: Example: findobjThe findobj command
Page 129 and 130: 3. Add the property you want to set
Page 131 and 132: is numbered from top to bottom. The
Page 133 and 134: axis ijUsually images like this do
Page 135 and 136: 32.2 Tick Marks and Labelsmatlab’
Page 137 and 138: clfaxes(’pos’,[.2 .1 .7 .4])x =
Page 139 and 140: property to [0 top] in the call to
Page 141 and 142: object’s HorizontalAlignment and
Page 143 and 144: the required symbols. The m-file ti
Page 145 and 146: 1. Use graphical elements that serv
Page 147 and 148: uicontrol(’Callback’,’ezplot(
Page 149 and 150: uicontrol(’Pos’,[110 280 60 19]
Page 151 and 152: ’String’,’0.5’,’Style’,
Page 153 and 154: function exradio(action)if nargin =
Page 155 and 156: fail. One place to put variables th
Page 157 and 158: 34.7 Fast DrawingFor fast drawing o
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controlled by guide and which are a
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InvertHardcopy: [ {on} | off ]Paper
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Another option is to use an image f
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yur is the y coordinate of the uppe
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\end{center}\caption{This is the fi
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x 294x1 ...y 294x1 ...z 294x1 ...Gr
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diagram. Such a triangular grid can
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xt = x([1 9 10 1]);yt = y([1 9 10 1
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x = [0 0 .5 0.5 .5 1 11 .5 .5 .5];y
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fac2 = [1 2 61 6 31 4 61 6 5];The r
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t = linspace(0,2*pi,20);x = cos(t);
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N = 20;dt = 2*pi/N;t = 0:dt:(N-1)*d
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colouring of the sphere itself. To
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material dullThe default is materia
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time taken by this routine to calcu
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first row of a by taking the column
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38.3 Debuggingmatlab has a suite of
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10: y = linspace(ycentre - L,ycentr
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We change variables:p ′ = C + Bx.
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Exercise 6 (Page 59)You can generat
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33 ! 36 $ 39 ’ 42 * 45 - 48 034 "
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R = 1; N = 200;[x,y] = meshgrid(lin
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(The plot might take a few seconds
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% Reproduce the layers at the diffe
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