INTRODUCTION TO MATLAB PLOTTING WITH MATLAB

Transcription

1 1 INTRODUCTION TO MATLAB PLOTTING WITH MATLAB Plotting with MATLAB x-y plot Plotting with MATLAB MATLAB contains many powerful functions for easily creating plots of several different types. Command plot(x,y) title( text ) Description Generates a plot of the array y versus the array x on rectilinear axes. Puts text in a title at the top of the plot. 2 xlabel( text ) Adds a text label to the horizontal axis (the abscissa). ylabel( text ) Adds a text label to the vertical axis (the ordinate). 1

2 Command [x,y] = ginput(n) Description Enables the mouse to get n points from a plot, and returns the x and y coordinates in the vectors x and y, which have a length n. 3 grid Legend( leg1, leg2, ) gtext( text ) axis axis([xmin XMAX YMIN YMAX]) sets scaling for the x- and y-axes on the current plot Puts grid lines on the plot. Creates a legend using the strings leg1 and leg2 and so on Enables placement of text with the mouse. Control axis scaling and appearance. 4 Plotting 2

3 Sample Plot Title Ylabel Grid Legend Xlabel 6 Example Use MATLAB to plot the function s=2sin(3t+2) over the interval 0 t 5. Put a title on the plot, and properly label the axes. The variable s represents speed in feet per second; the variable t represents time in seconds 3

4 s=2*sin(2*t+3) Sine wave 1 s(speed(feet/s)) Plot sine wave t(seconds) 4

5 9 Specifying Line Styles and Colors It is possible to specify color, line styles, and markers (such as plus signs or circles) when you plot your data using the plot command: plot(x,y,'color_style_marker') For example: plot(x,y,'r:+') plots a red-dotted line and places plus sign markers at each data point. Two plots on the same graph 10 >> x= 0:pi/100:2*pi; >> y1= cos(x*4); >> plot(x,y1), title('two Plots on the Same Axis'), >> xlabel('angle, radians'), grid >> y2= sin(x); >> hold on; >> plot(x,y2) Two Plots on the Same Axis angle, radians 5

6 Example Data Markers and Line Types To plot y versus x with a solid line and u versus v with a dashed line, type plot(x, y, u, v, -- ), where the symbols -- represent a dashed line. To plot y versus x with asterisks (*) connected with a dotted line, you must plot the data twice by typing : plot (x, y, *, x, y, : ). To plot y versus x with green asterisks (*) connected with red dashed line, you must plot the data twice by typing: plot(x, y, g*,x, y, r-- ). 6

7 Line Styles Plot Options Colors Page (115) 7

8 15 Basic Plotting Functions The plot function has different forms, depending on the input arguments. If y is a vector, plot(y) produces a piecewise graph of the elements of (y) versus the index of the elements of (y). If you specify two vectors as arguments, plot(x,y) produces a graph of y versus x. You can also label the axes and add a title, using the xlabel, ylabel, and title functions. Example: xlabel('x = 0:2\pi') ylabel('sine of x') title('plot of the Sine Function','FontSize',12) 16 8

9 17 Example: Create x as a vector of linearly spaced values between 0 and 2pi. Use an increment of pi/100 between the values. a) Create y as sine values of x. b) Create a line plot of the data. Answer: x = 0:pi/100:2*pi; y = sin(x); plot(x,y) 18 Example: Define x as 100 linearly spaced values between -2pi and 2pi. Define y1 and y2 as sine and cosine values of x. Create a line plot of both sets of data. Answer: x = linspace(-2*pi,2*pi); y1 = sin(x); y2 = cos(x); figure plot(x,y1,x,y2) 9

10 19 Example: Plot three sine curves with a small phase shift between each line. Use the default line style for the first line. Specify a dashed line style for the second line and a dotted line style for the third line. Answer: x = 0:pi/100:2*pi; y1 = sin(x); y2 = sin(x-0.25); y3 = sin(x-0.5); figure plot(x,y1,x,y2,'--',x,y3,':') 20 Example: Plot three sine curves with a small phase shift between each line. Use a green line with no markers for the first sine curve. Use a blue dashed line with circle markers for the second sine curve. Use only cyan star markers for the third sine curve. Answer: x = 0:pi/10:2*pi; y1 = sin(x); y2 = sin(x-0.25); y3 = sin(x-0.5); figure plot(x,y1,'g',x,y2,'b--o',x,y3,'c*') 10

11 21 Plotting Multiple Data Sets in One Graph Multiple x-y pair arguments create multiple graphs with a single call to plot. For example: x = 0:pi/100:2*pi; y = sin(x); y2 = sin(x-.25); y3 = sin(x-.5); plot(x,y,x,y2,x,y3) 22 Figure Windows Graphing functions automatically open a new figure window if there are no figure windows already on the screen. To make a figure window the current figure, type figure(n) where n is the number in the figure title bar. The results of subsequent graphics commands are displayed in this window. 11

12 MATLAB functions & plotting task: related to chp3 & 4 Plot the function sin(x) between 0 x 4π Create an x-array of 100 samples between 0 and 4π. 23 >>x=linspace(0,4*pi,100); Calculate sin(.) of the x-array >>y=sin(x); Plot the y-array >>plot(y) Note: The linspace function generates linearly spaced vectors. It is similar to the colon operator ":", but gives direct control over the number of points. 24 Plot the function e -x/3 sin(x) between 0 x 4π Create an x-array of 100 samples between 0 and 4π. >>x=linspace(0,4*pi,100); Calculate sin(.) of the x-array >>y=sin(x); Calculate e -x/3 of the x-array >>y1=exp(-x/3); Multiply the arrays y and y1 >>y2=y*y1; 12

13 25 Plot the function e -x/3 sin(x) between 0 x 4π Multiply the arrays y and y1 correctly >>y2=y.*y1; Plot the y2-array >>plot(y2) Display Facilities plot(.) Example: >>x=linspace(0,4*pi,100); >>y=sin(x); >>plot(y) >>plot(x,y) stem(.) Example: >>stem(y) >>stem(x,y)

14 27 Display Facilities title(.) >>title( This is the sinus function ) xlabel(.) >>xlabel( x (secs) ) ylabel(.) sin(x) This is the sinus function >>ylabel( sin(x) ) x (secs) 28 More examples about MATLAB functions & plotting task: related to chp3 & 4- Assignment plot xlabel ylabel title grid axis stem subplot Z = [0 : pi/50 : 10*pi]; X = exp(-.2.*z).*cos(z); Y = exp(-.2.*z).*sin(z); plot3(x,y,z); grid on; xlabel('x-axis'); ylabel('y-axis'); zlabel('z-axis'); 14

15 29 Ex1; Temperature analysis & plot as Problem Solving & plotting (this example is given page20 chp1), but better for student to take it after understanding MATLAB commands given in Chp2,3,4: Write MATLAB code to plot given Table below: Assignment MATLAB Code Solution for temperature data (very important as first case study & MATLAB application, student should run & save code as m.file practically in Lab session) 30 % Compute average & plot temperature data time = [0.0,0.5,1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5,5]; temps=[105,126,119,..., 137]; average = mean(temps); plot(time, temps), title ( temperature distribution ), xlabel( Time, Minutes ), ylablel( temp, degree C ), grid 15

16 31 Output graph of temperature distribution & average = for given input. EX3: Create an M-File to plot y2= sin(x)* exp(-x/3) Save file as M106.m 32 If you include ; at the end of each statement, result will not be shown immediately 16

17 Plot PLOT Linear plot. PLOT(X,Y) plots vector Y versus vector X PLOT(Y) plots the columns of Y versus their index PLOT(X,Y,S) with plot symbols and colors See also SEMILOGX, SEMILOGY, TITLE, XLABEL, YLABEL, AXIS, AXES, HOLD, COLORDEF, LEGEND, SUBPLOT... Example x = [ ]; y1 = (x.^2) -1; plot(x, y1,'bo-.'); 33 Plot Properties XLABEL X-axis label. XLABEL('text') adds text beside the X-axis on the current axis. Example... xlabel('x values'); ylabel('y values'); YLABEL Y-axis label. YLABEL('text') adds text beside the Y-axis on the current axis

18 Hold on: Adding Plots to an Existing Graph HOLD Hold current graph. HOLD ON holds the current plot and all axis properties so that subsequent graphing commands add to the existing graph. Example... hold on; y2 = x + 2; plot(x, y2, 'g+:'); HOLD OFF returns to the default mode HOLD, by itself, toggles the hold state. When you type: hold on MATLAB does not replace the existing graph when you issue another plotting command; it adds the new data to the current graph, rescaling the axes if necessary. 35 Subplot SUBPLOT Create axes in tiled positions. SUBPLOT(m,n,p), or SUBPLOT(mnp), breaks the Figure window into an m-by-n matrix of small axes Example x = [ ]; y1 = (x.^2) -1; % Plot y1 on the top subplot(2,1,1); plot(x, y1,'bo-.'); xlabel('x values'); ylabel('y values'); % Plot y2 on the bottom subplot(2,1,2); y2 = x + 2; plot(x, y2, 'g+:'); 36 18

19 37 You can use the subplot command to obtain several smaller subplot in the same figure. The syntax is subplot (m,n,p). This command divides the Figure window into an array of rectangular panes with m rows and n columns. The variable p tells MATLAB to place the output of the plot command following the subplot command into the path pane. Displaying Multiple Plots in One Figure subplot(m,n,p) This splits the figure window into an m-by-n matrix of small subplots and selects the path subplot for the current plot. Example: t = 0:pi/10:2*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) 38 19

20 Subplots Syntax: subplot(rows,cols,index)»subplot(2,2,1);»»subplot(2,2,2)»...»subplot(2,2,3)»...»subplot(2,2,4)»... Figure FIGURE Create figure window. FIGURE, by itself, creates a new figure window, and returns its handle. Example x = [ ]; y1 = (x.^2) -1; % Plot y1 in the 1 st Figure plot(x, y1,'bo-.'); xlabel('x values'); ylabel('y values'); % Plot y2 in the 2 nd Figure figure y2 = x + 2; plot(x, y2, 'g+:'); 40 20

21 41 Figure 7.3 The graphics window opened on top of the command window. (This graphics window can be resized to a convenient size.) 42 Figure 7.8 Multiple plots with adjusted line, mark, and color type. 21

22 43 Figure 4.13 Linear and logarithmic plots D display variants Cartesian coordinates >> bar(x,y) % vertical bar graph >> barh(x,y) % horizontal bar graph >> stem(x,y) % stem plot >> area(x,y) % color fill from horizontal axis to line >> hist(y,n) % histogram with N bins (default N = 10) 22

23 Three-Dimensional Plots Surface Plot x = 0:0.1:2; y = 0:0.1:2; [xx, yy] = meshgrid(x,y); zz=sin(xx.^2+yy.^2); surf(xx,yy,zz) xlabel('x axes') ylabel('y axes') Contour Plots contourf-colorbar-plot3-waterfall-contour3-mesh-surf 46 23

24 7.3 Editing Plots from the Menu Bar Plotting from the workspace window

25 Plotting Example 49 A basic plot >> x = [0:0.1:2*pi] >> y = sin(x) >> plot(x, y, r.- ) Plotting Example 50 Plotting a matrix MATLAB will treat each column as a different set of data

26 Plotting Example 51 >> x = [0:0.1:2*pi]; >> y = sin(x); >> plot(x, y, 'b*-') Sin Plots sin(x) 2*sin(x) >> hold on >> plot(x, y*2, r.-') >> title('sin Plots'); >> legend('sin(x)', '2*sin(x)'); >> axis([ ]) >> xlabel( x ); >> ylabel( y ); y x >> hold off 51 Plotting Example 52 Plotting data >> results = rand(10, 3) >> plot(results, 'b*') >> hold on >> plot(mean(results, 2), r.- )

27 Plotting Example 53 Error bar plot >> errorbar(mean(data, 2), std(data, [], 2)) 1 Mean test results with error bars