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MatLAB Lesson 3 : Graphics

MatLAB Lesson 3 : Graphics. Edward Cheung email: icec@polyu.edu.hk Room W311g. 2008m. Plotting. Graph is more easy to be read then table in particular to grasp the relationships among variables Horizontal axis is a control variable Plots are normally done in two dimensions

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MatLAB Lesson 3 : Graphics

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  1. MatLABLesson 3 : Graphics Edward Cheung email: icec@polyu.edu.hk Room W311g 2008m

  2. Plotting • Graph is more easy to be read then table in particular to grasp the relationships among variables • Horizontal axis is a control variable • Plots are normally done in two dimensions • Plot File Formats • .fig • MatLab format – double click to open • jpg/bmp/tiff…etc • raster image formats for inserting into reports

  3. Simple Graph • Plot graph >> x=0:5; y=0:10:50; plot(x,y) • Always add title & label all axis – Meaning & Unit!!! >> xlabel('time taken (sec)') ylabel('Distance Travelled (m)') title('Speed of Test Vehicle') title(‘Speed of Mark’’s Vehicle’) % note double apostrophe for Mark‘s • A new plot() will erase previously defined labels and title

  4. Single Variable Plotting >> z=sin(0:0.1:2*pi);plot(z) What is the size of sample? >> size(z) ans = 1 63 % 1 Dimension 63 Elements >> xlabel('t (0.1 radian)'); ylabel('z'); title('Function of z') • Note the colour cue when typing (')s - “A hint of warning on typing mistake”

  5. Figure Copy Template Setting • Menu  File  Preference

  6. Plot More Than One Variable on Same Graph % Try example as follows:- x=0:pi/100:2*pi; %set an array x range 2Pi y1=sin(x); % y1 is the first function plot(x,y1) y2=sin(x-pi/4); % y2 is the second function hold on % don’t clear the graph plot(x,y2) % plot second graph y3=sin(x-pi/2); % y3 is the third function pause(5) % wait 5 seconds plot(x,y3) % plot y3 on same graph y4=sin(x-pi); % y4 is the last one pause % wait for pressing key plot(x,y4) % then plot y4 hold off % clear the hold % same colour because ‘hold off’ is used

  7. Plot more than one function on a graph % Example (multi-colour plot):- x=-10:10; y=x.^2; plot(x,y,x,2*y,x,3*y,x,4*y) h=findobj(gcf,'linewidth',.5); set(h,'linewidth',2) grid Usage:- Set(h,’property_name’, ‘property_value’) H=gcf % get current figure handle (e.g. H=1) findobj(‘object_handle’,’property_name’,’property_value’)

  8. Basic Plotting/Formatting Functions • help graphics • plot(x,y,’linestyle_marker_colour’) – creates an x-y plot • title(‘string’) – add title to a plot • xlabel(‘string’) – label x-axis • ylabel(‘string’) – label y-axis • grid – grid on/off • pause – pauses the execution of the program and allow the user to read the graph • figure – create/index for graph reference >> figure(2) • hold – on/off – freeze the current plot to allow overlaid • clf – clear current figure

  9. Graph Formating • Line style, colours & markers can be specified with the plot(x,y,s) command S is a character string made from one element • Usage of line types, plot symbols and colors are given in the help page >> help plot • Example >> x=0:0.1:2*pi; y=sin(x); plot(x,y,':sg') % colon=>dotted line • Line style, colours & markers are independent parameters and all must be specified for plotting

  10. Properties of Graphics >>get(gcf) % return current figure properties >>get(gca) % return current axis properties • Linewidth is a scale object • The width of the line object. Specify this value in points (1 point = 1/72 inch). The default LineWidth is 0.5 point. >>set(gca,'linewidth',4) % set line width

  11. Marker Properties • MarkerSize. The size of the marker, in points. • The default value is 6 pts • The point marker drawn at 1/3 of the specified size • MarkerFaceColor. The fill colour for markers that are closed shapes (circle, square, diamond, pentagram, hexagram, and the four triangles). • none = interior of the marker transparent • auto = same colour as the axis • MarkerEdgeColor. The colour of the marker or the edge colour for filled markers (circle, square, diamond, pentagram, hexagram, and the four triangles). • none = no colour, which makes non-filled markers invisible • auto = same colour as the line

  12. Example on the Properties of Markers x=-pi:pi/10:pi; y=tan(sin(x))-sin(tan(x)); plot(x,y,'--rs','Linewidth',2,... 'MarkerEdgeColor','k','MarkerFaceColor','g','MarkerSize',10)

  13. Multiple Plots per Figure • Subplot(m,n,i) breaks the figure into an m-by-n matrix of smaller plots and numbered in row to column >> subplot 221 % 2 x 2 plot #1 t=linspace(0,2*pi,4); % t->x axis range 2pi plot(sin(t)) % a poor resolution plot • y = linspace(a,b,n) generates a row vector y of n points linearly spaced between and including a and b. • when n is not specified, n=100 • function similar to the colon operator • For a better resolution set n=100 >> t1=linspace(0,2*pi); subplot 222 plot(sin(t1))

  14. Multiple Plots Per Figure (Cont.) • Set x axis to radian >> subplot 223 plot(t1,sin(t1)) • Suppose we want the data to fill the axes >> subplot 224 plot(t1,sin(t1)) axis tight % set axes limit to data range • axis auto/tight/equal/square/off/on • Axes control function >> axis([xmin xmax ymin ymax]) Sets the limit for x & y axes of the current plot

  15. Axis Limits • Change axes for a zoom in plot x=0:.01:30; subplot(211) plot(x,x.*sin(x)) subplot(212) plot(x,x.*sin(x)) axis([10 20 -20 20])

  16. Three Plots In One Graph • Example: plotting an underdamped function in 3 views (P.23) >> x=linspace(0,1); y=exp(-x).*cos(6*pi*x); w=exp(-x); z=-w; subplot(2,2,1) plot(x,y) subplot(2,2,2) • >> plot(x,w,'r:',x,z,'r:') • subplot(2,1,2) • plot(x,y,x,w,'r:',x,z,'r:')

  17. Multiple Plots per Figure with Window Plot x=0:0.05:2*pi; y=sin(x); subplot(2,1,1) plot(x,y,'r') subplot(2,1,2) plot(x,y,'b') axis off axes('Position', [0.6 0.2 0.3 0.2]) plot(x,y,'g')

  18. Axes • Axes() • Is a function that can be used to create an axes graphics object in the current figure using default property values. • The axes Position property enables the user to define the location of the axes within the figure window. • h = axes('Position',position_rectangle) • axes('position', rect) opens up an axis at the specified location • rect= [left, bottom, width, height] specifies the location and size of the side of the axis box, relative to the lower-left corner of the Figure window, in normalized units where (0,0) is the lower-left corner and (1.0,1.0) is the upper-right.

  19. Additional Graph Formatting Functions • Title(‘string) % discuss already • Add legend to a graph >>legend(‘string1’, ‘string2’,…) >>legend(‘off’) >>legend(…,pos) >>help legend % give usage • Arrow & special characters, Greek characters • Annotation with text() >>text(x,y,‘string1’) • Add string at (x,y) >>gtext(‘string’) • Add string at mouse click interactively

  20. Example - Title, Legend, Label & Text Function >> % Example disp('formatting graph') t=-pi:0.1:pi; plot(t,sin(t),t,cos(t)) title('Function of Sine and Cosine','FontSize',18) xlabel('t=-\pi to \pi','FontSize',16) ylabel('sin(t) & cos(t)','Fontsize',16) legend('Sine','Cosine') text(-1,sin(-1),'sin(t)') text(2,cos(2),'cos(t)')

  21. With Symbol & Greek Letters in Text Strings >>% example p.26 t=0:900; plot(t,0.25*exp(-0.005*t)) title('A{\ite}^{\alpha{\itt}}','FontSize',16) ylabel('Amplitude','FontSize',16) xlabel('Time\mu sec','FontSize',16) text(300,0.25*exp(-0.005*300),'\bullet\leftarrow0.25{\ite}^{-0.005{\itt}}at {\itt}=300','FontSize',14)

  22. Text Properties • Search for ‘text properties’ in help can get the table of character sequence for Greek or mathematic symbols • TeX compatible • TeX is a cross-platform typesetting freeware • Reference card • http://refcards.com/refcards/tex/tex-refcard-letter.pdf • What fonts are available? >> c=listfonts % return available fonts • Try (put abc… on a plot using gtext):- >> gtext('\fontname{roman}\fontsize{20}abc') gtext('\fontname{arial}\fontsize{20}\bfabc\fontsize{10}\beta\phi')

  23. Axis Ticks t=0:100; plot(t,sin(t/100*2*pi)); set(gca,'XTick',0:5:100) grid

  24. Axis Tick (cont. example) labels={'0',' ','10',' ','20',' ','30',' ','40',' ','50',' ','60',' ','70',' ','80',' ','90',' ','100'} set(gca,'XTickLabel',labels)

  25. Example on Tick & Labels temp=[21.1 22.2 19.4 23.3 23.9 21.1 20]; days={'sun','mon','tue','wed','thur','fri','sat'}; plot(1:7,temp); axis([1 7 16 26]) set(gca,'XTickLabel',days); grid title('Temperature','FontSize',16)

  26. Bar Chart • BAR(Y) uses the default value of X=1:M. For vector inputs, BAR(X,Y) or BAR(Y) draws LENGTH(Y) bars. The colors are set by the colormap. • BAR(X,Y,WIDTH) or BAR(Y,WIDTH) specifies the width of the bars. Values of WIDTH > 1, produce overlapped bars. The default value is WIDTH=0.8 • BAR(...,'grouped') produces the default vertical grouped bar chart. • BAR(...,'stacked') produces a vertical stacked bar chart. • BARH Horizontal bar graph • BAR3 3-D bar graph • BAR3H Horizontal 3-D bar graph

  27. Example on Bar Chart Y=round(rand(5,3)*10) subplot 221 bar(Y) title('Group') subplot 222 bar(Y,'stack') title('stack') subplot 223 barh(Y,'stack') title('stack') subplot 224 bar(Y,1.5) title('width=1.5')

  28. Example on Bar Chart

  29. Example on Bar3 Y=cool(7); subplot(2,2,1) bar3(Y) title('Default') subplot(2,2,2) bar3(Y,'group') title('Group') subplot(2,2,3) bar3(Y,'stack') subplot(2,2,4) bar3h(Y,'stack') % COOL(M) returns an M-by-3 matrix containing a "cool" colormap.

  30. Example – bar3h

  31. Example on Filled Area Plots % An area plot displays elements in Y as one or more curves and fills the area beneath each curve. sales=[51.6 82.4 90.8 59.1 47]; x=90:94; profits=[19.3 34.2 61.4 50.5 29.4]; area(x,sales,'FaceColor',[.5 .9 .6],'EdgeColor','b','LineWidth',2) hold on area(x,profits,'FaceColor',[.9 .85 .7],'EdgeColor','y','LineWidth',2) hold off set(gca,'XTick',[90:94]) text(92,20,'Expenses') text(91,60,'Profits')

  32. Example on Area Filled Plot

  33. Example on Pie Charts x=[1 3 0.5 2.5 2]; explode=[0 1 0 0 0]; subplot 221 pie(x) % pie chart title('2D-Default') subplot 222 pie(x,explode) % explode pie chart title('2D-explode') subplot 223 pie3(x) % 3D pie chart title('3D-Default') subplot 224 pie3(x,explode) % 3D explode pie chart title('3D-Default')

  34. Example on Pie Charts

  35. Example on Histograms X=randn(10000,3); subplot(2,1,1) hist(X) title('Histogram showing 10 bins') subplot(2,1,2) hist(X,20) title('Histogram showing 20 bins')

  36. Example on Histograms

  37. Example on Compass Plot • COMPASS(U,V) draws a graph that displays the vectors with components (U,V) as arrows emanating from the origin. x=floor(randn(10,1)*10) y=floor(randn(10,1)*10) compass(x,y)

  38. Compass Plot (Cont. example) z=[-0.9+5i,-0.9-5i,2.6+3.2i,2.6-3.2i, 3.4811, 1.6+3.2i,1.6-3.2i,-4.3,-0.6+2.7i,-0.6-2.7i] compass(z)

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