Basic Graphs. Dmitry Adamskiy 16 November 2011

Transcription

1 Basic Graphs Dmitry Adamskiy 16 November 211 1

2 Plot Function plot(x,y): plots vector Y versus vector X X and Y must have the same size: X = [x1, x2 xn] and Y = [y1, y2,, yn] Broken line that connects points (x1, y1), (x2, y2),, (xn, yn) If X is a scalar x and Y is a vector [y1,, yn], n disconnected points (x, y1), (x, y2),, (x, yn) are plotted. 2

3 Example x = :1/4:2; y = sin (x); plot (x, y)

4 Types of Lines plot(x,y,linespec) LineSpec is a string that determines line specifications (any or all of them): line type: - solid, : dotted, -. dashdot, -- dashed, (none) no line colour: b blue, g green, r red, k black marker symbol:. point, o circle, x x-mark, + plus Examples: plot (X,Y, k+:') plots a black dotted line with a plus at each data point; plot (X,Y,'bo') plots blue circles at each data point but does not draw any line. For full list of options, type help plot 4

5 More on plot To plot different graphs on one figure, we use the hold on command. Example hold on plot (x, cos(x), 'g-' ) title('sin and cos functions') legend('sin(x)', 'cos(x)') xlabel('x') ylabel('y') 5

6 The SIN and COS graphs (1) The Title 1.8 sin and cos functions sin(x) cos(x) The y Label y The Legend x 6 The x Label

7 The SIN and COS graphs (2) We can have the grids on too. Use grid on sin and cos functions sin(x) cos(x).4.2 y x

8 Cleaning Up Use close all to close all figure windows Use clf to clear a current figure window Use cla to clear axes in a current figure 8

9 Exercises (1) Make sure you type clear all and close all before starting Let s try plotting some graphs a) Generate a vector X with values from 1 to 1 b) Generate a vector Y containing X squared c) Generate a vector Z containing X*9 9

10 Exercises (2) d) Plot Y against X, using a red line with stars at each data point (type help plot if you need to) e) Keep that plot, and on the same graph plot Z against X using a green line with squares at each point f) Give your figure a title and a legend 1

11 More on plot (2) Multiple x-y pairs create multiple graphs with a single call to plot Example: plot(x1,y1,x2,y2,x3,y3) MATLAB automatically cycles through a predefined list of colours to allow discrimination between each set of data 11

12 Example >> t = : pi/1 :2*pi ; >> y = sin(t) ; >> plot (t,y) >> y2 = sin(t -.25); >> y3 = sin(t -.5); >> plot(t,y,t,y2,t,y3) 12

13 plot(t,y) plot (t,y,t,y2,t,y3)

14 Figure Window (1) The plot function automatically opens a new figure window if there are no figure windows already on the screen. If a figure window exists, plot uses that window by default. To open a new figure window and make it the current figure type figure 14

15 Figure Window (2) To make an existing figure window the current figure, type figure(n) where n is the number in the figure title bar. The result of subsequent graphics commands are displayed in this window. 15

16 Subplots The subplot function allows you to display multiple plots in the same window or print them on the same piece of paper. Typing subplot(m,n,p) breaks the figure window into an m-by-n matrix of small subplots and selects the pth subplot for the current plot. 16

17 Saving Plots Plots can be saved in files with extension.fig Other options: eps, pdf jpg, bmp, tif 17

18 Example >> t = : pi/1: 2*pi >> [X,Y,Z] = cylinder(4*cos(t)); >> subplot(2,2,1) >> mesh(x) >> subplot(2,2,2); mesh(y) >> subplot(2,2,3); mesh(z) >> subplot(2,2,4); mesh(x,y,z) 18

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20 Controlling Axes The axis function has a number of options for customizing the scaling, orientation, and aspect ratio of plots. Ordinarily MATLAB finds the minima and maxima of the data and chooses an appropriate plot box and axes labeling. The axis function overrides the default by setting custom axis limits. 2

21 The axis function axis([xmin xmax ymin ymax]): sets scaling for the x and y axes on the current plot axis auto: returns the axis scaling to its default, automatic mode. axis off: turns off the axis labeling axis on: turns on the axis labeling axis square: makes the current axis box square in size. 21

22 Example >> t = : pi/1 :2*pi ; >> y = sin(t) ; >> plot(t,y) >> axis([ 2*pi -2 2])

23 Axis Labels and Titles The xlabel, ylabel and zlabel functions add x, y, and z-axis labels. The title function adds a title at the top of the figure and text function inserts text anywhere in the figure. A subset of TeX notation produces Greek letters, mathematical symbols and alternate fonts. 23

24 Example >> t = -pi: pi/1 : pi; >> y =sin(t); >> plot(t,y) >> axis([-pi pi -1 1]) >> xlabel( -\pi \leq {\it t} \leq \pi ) >> ylabel( sin(t) ) >> title( Graph of the sine function ) >> text(1,-1/3, \it{note the odd symmetry.} ) 24

25 Example Cont d 1 Graph of the sine function sin(t) Note the odd symmetry π t π 25

26 Another Way To Edit Figures Click the icon Show plot tools and dock figure 26

27 Exercises Make sure to clear all before you begin. Plot the graphs of the following functions on different figures. x is a vector of real numbers ranging from -1 to 1 inclusive, created with.1 steps. 27 y = sin(x)/x x 3 y = tan(x) y = y = x y = y = y = log(x) x e 2 x

28 Acknowledgements In the preparation of the material for this handout use has been made of the following sources: MATLAB 7 manuals ers/ahamilton/matlab.htm 28