Basics of MATLAB and Beyond

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m = gray(8);colormap(m)imagesc(1:1000)Most of matlab’s surface viewing functions use the colour map to applycolour to the surface depending on the z-value. The imagesc functionproduces a coloured image of the matrix argument, colouring each elementdepending on its value. The smallest element will take the colourspecified in the first row of the colour map, the largest element will takethe colour specified in the last row of the colour map, and all the elementsin between will take linearly interpolated colours.To get a plot of the levels of red, green, and blue in the current colourmap use rgbplot:colormap(summer)rgbplot(colormap)On the screen the lines corresponding to the red, green, and blue componentsof the colour map are coloured red, green, and blue, respectively.7.3 Colour BarTo display the current colour map use the colorbar function:z = peaks;colormap(gray(8))imagesc(z)colorbar7.4 Good and Bad Colour MapsMuch research has been done on human perception of colours and, in particular,how different viewers interpret coloured images as value-scales.c○ 2000 by CRC Press LLC
The conclusion is that most viewers find it very difficult to interpretthese sorts of images; the cognitive switch from, for example, roygbivto amplitude is very slow and nonintuitive. A way out of this isto use a palette of slightly varying, nonsaturated colours. These sortsof colours have been used to create high-quality geographic maps formany years. Most of matlab’s colour maps consist of highly saturatedcolours (including the default colour map, which is jet(64)). It is betterto forgo these sorts of colour maps and stick with the calmer onessuch as gray, bone, orsummer. The gray colour map has the addedadvantage that printed versions will reproduce easily, for example, on aphotocopier. 2 The companion m-files include some other colour maps:redblue, myjet, yellow, green, red, and blue.To distinguish adjacent patches of subtly different colours, the eyecan be helped by enclosing the patches with a thin dark edge. Thecontourf function, therefore, is an excellent way of displaying this sortof data. 37.5 Extracting Logical DomainsLet us look again at the peaks function:[x,y,z] = peaks;surfl(x,y,z)axis tightcolormap(gray(64))Suppose we want to extract the part of this surface for which the z valueslie between 2 and 4. We use exactly the same technique as was givenon page 23. The find command is used first to find the indices of the zvalues that satisfy the logical test:>> ind = find(2 size(ind)ans =234 1There are 234 elements in z that satisfy our condition. We can plot theseelements over the surface as follows:2 Edward R. Tufte, Visual Explanations (Graphics Press, Cheshire Connecticut,1997), pp. 76–77.3 Edward R. Tufte, Envisioning Information (Graphics Press, Cheshire Connecticut,1990), pp. 88ff.c○ 2000 by CRC Press LLC
Page 2 and 3: BASICS OFMATLAB®and Beyondc○ 200
Page 4 and 5: Library of Congress Cataloging-in-P
Page 6 and 7: typing pwd (print working directory
Page 8 and 9: ContentsIBasics of MATLAB1 First St
Page 10 and 11: 20 Time-Frequency Analysis21 Line A
Page 12 and 13: 39Answers to Exercises (Part I)40 A
Page 14 and 15: Set → Getting Started with MATLAB
Page 16 and 17: 1.5 The Colon OperatorTo generate a
Page 18 and 19: matlab will recall the last command
Page 20 and 21: a = zeros(2,3)a =0 0 00 0 0>> b = o
Page 22 and 23: [a a(a)]ans =1 2 3 1 4 74 5 6 2 5 8
Page 24 and 25: a + bans =11 3344 6677 993.8 Transp
Page 26 and 27: 4.2 Adding PlotsWhen you issue a pl
Page 28 and 29: x = [[1 2 3 4]’ [2 3 4 5]’ [3 4
Page 30 and 31: 4.7 AxesSo far we have allowed matl
Page 32 and 33: v =1122>> v*uans =1 2 0 11 2 0 12 4
Page 34 and 35: max returns a vector containing the
Page 36 and 37: s = 100*spiral(3)s =700 800 900600
Page 38 and 39: We can plot the surface z as a func
Page 40 and 41: The contour function plots the cont
Page 44 and 45: hold onplot3(x(ind),y(ind),z(ind),
Page 46 and 47: z = 5*ones(3,3)z =5 5 55 5 55 5 5>>
Page 48 and 49: contour(x,y,z,30);You may have noti
Page 50 and 51: variables that are local to themsel
Page 52 and 53: SwitchThe basic form of a switch st
Page 54 and 55: i =i =123136Vectorised Codematlab i
Page 56 and 57: 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
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eval(str)v =1 2 3 4 5The eval(str)
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Inline objects, like every other ma
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a(1,1) = {[1 2 3]}a =[1x3double]or>
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t = {’help’ spiral(3) ; eye(2)
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meteo.Temperatureans =24ans =19.000
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3 >> a = [1 2 ;4 5 6;7 8 9]a =1 2 3
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[x,y] = meshgrid(1:5,1:3)x =1 2 3 4
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ans(:,:,2) =999And to sum over “p
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An Application of RGB ImagesTo see
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You can see that over the 8 time st
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name>> staff(2,1,2).name(5:9)ans =B
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q =7 8 96 1 25 4 3>> save saved_dat
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fid = fopen(’asc.dat’);The fope
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display and the enclosed area is th
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MarkerEdgeColor = auto(and so on)In
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text(-.7,f(-.7),’f(X)’)But we h
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plt(x,f(x/2),’--’)Let us try ca
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Example: findobjThe findobj command
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3. Add the property you want to set
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is numbered from top to bottom. The
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axis ijUsually images like this do
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32.2 Tick Marks and Labelsmatlab’
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clfaxes(’pos’,[.2 .1 .7 .4])x =
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property to [0 top] in the call to
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object’s HorizontalAlignment and
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the required symbols. The m-file ti
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1. Use graphical elements that serv
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uicontrol(’Callback’,’ezplot(
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uicontrol(’Pos’,[110 280 60 19]
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’String’,’0.5’,’Style’,
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function exradio(action)if nargin =
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fail. One place to put variables th
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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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