Two-dimensional Plots

Transcription

1 Two-dimensional Plots ELEC 206 Prof. Siripong Potisuk 1 The Plot Command The simplest command for 2-D plotting Syntax: >> plot(x,y) The arguments x and y are vectors (1-D arrays) which must be of the same length, but any type x contains data points along the horizontal axis y contains data points along the vertical axis When executed, a figure window pops up containing the figure with the graph of y vs. x 2 1

2 The Figure Window Every time a plot command is issued, MATLAB checks if a figure window is currently opened If one is, MATLAB will erase the plot in it and draw a new one. If none is, a new figure window pops up and a graph drawn in it If multiple windows are opened, MATLAB will draw in the latest one 3 The Figure Window To specify the figure window number, use >> figure(n) where n is an integer indicated the figure number If figure window n exists, makes it the active window If figure window n doesn't exist, creates it and makes it the active window If n is omitted, the new figure window will be labeled figure n where n is the integer greater than the current active figure number by 1 4 2

3 If after issuing a plot command and no figure window appears, it is buried. Click on the figure window icon on the task bar to make the window appear 5 Closing Figure Window Use close command to close figure windows - close closes active Figure Window - close(n) closes Figure Window n - close all closes all open Figure Windows Use clf command to clear contents of the current figure window Use clf(n) command to clear contents of the n th figure window 6 3

4 >> yr = 1988:1994; >> sales = [ ]; >> plot(yr,sales) 7 >> x = 1:10; >> y = x.^2 >> plot(x,y) Blue is the default line color Points connected by straight lines with no point markers Both axes are linear 8 4

5 Optional Arguments The vector x can be omitted Syntax: >> plot(y) MATLAB creates a plot of the vector y on the vertical axis against a set of numbers from 1 to n where n is the number of elements of y on the horizontal axis, i.e., a plot of y against its indices 9 >> y=[ ]; >> plot(y) 10 5

6 Important parts of a 2-D plot 11 Changing Default Settings 12 6

7 Line Specifiers define style and color of lines, and marker types

8 15 Property Name and Values 16 8

9 >> yr = 1988:1994; >> sales = [ ]; >> plot(yr,sales, --r*, linewidth,2,... markersize,12) Exporting the Figure To copy the entire figure window into another program, e.g., Word, PowerPoint 1. Click on the figure window to make it current window 2. Press ALT+PRNTSCRN 3. Paste into other application To copy just the plot area into another program, e.g., Word, PowerPoint 1. In figure window, select Edit, then Copy Figure 2. Paste into other application 18 9

10 Superimposing Multiple Graphs Plot two or more graphs on the same plot as follows (e.g., for three graphs) plot(x,y,u,v,t,h) Plots y vs. x, v vs. u, and h vs. t Vectors of each pair must be of the same size Different pairs can be of different sizes Can use line specifiers by putting in triplets (xdata, y-data, specifier), e.g., plot(x,y,'-b',u,v,'--r','t,h,'g:') 19 x=[-2:0.01:4]; y=3*x.^3-26*x+6; yd=9*x.^2-26; ydd=18*x; figure(2) plot(x,y,'-b',x,yd,'--r',x,ydd,':k') 20 10

11 Superimposing Multiple Graphs Normally, each time you execute plot, MATLAB erases a previous plot and draws a new one. To change this behavior: Draw the first graph with plot Issue the command hold on Call plot for each of the remaining graphs Issue the command hold off Graphs drawn after hold on are added to plot Graphs drawn after hold off erase plot 21 x=[-2:0.01:4]; y=3*x.^3-26*x+6; yd=9*x.^2-26; ydd=18*x; figure(2) plot(x,y,'-b') hold on plot(x,yd,'--r') plot(x,ydd,':k') hold off % create the first % graph of y % superimpose the % second graph of yd % superimpose the % third graph of ydd 22 11

12 Superimposing Multiple Graphs The line command adds additional graphs to an existing plot Syntax: line(x,y,'propertyname','propertyvalue') Example: line(x,y,'linestyle','--','color','r', 'marker','o') adds graph drawn with dashed red line and circular markers to current plot 23 x=[-2:0.01:4]; y=3*x.^3-26*x+6; yd=9*x.^2-26; ydd=18*x; figure(2) % create the first graph of y plot(x,y,'-b') % % superimpose the second graph of yd line(x,yd,'linestyle','--','color','r') % % superimpose the third graph of ydd line(x,ydd,'linestyle',':','color','k') 24 12

13 Making Multiple Plots in the Same Figure The subplot command divides the current active Figure Window into m rows and n columns of subplots Syntax: subplot(m,n,p) p in the subplot command refers to the numbering of subplots starting from left to right and row by row from top to bottom 25 The Subplot Command If subplots don't exist, subplot(m,n,p) creates them and makes subplot p the current subplot If subplots exist, subplot makes subplot p the current one When subplot defines current subplot, next plot and formatting commands draw in this current subplot 26 13

14 x=[-2:0.01:4]; y=3*x.^3-26*x+6; yd=9*x.^2-26; ydd=18*x; figure(3) subplot(3,1,1); plot(x,y,'-b') % graph of y subplot(3,1,2); plot(x,yd,'--r') % graph of yd subplot(3,1,3); plot(x,ydd,':k') % graph of ydd 27 Logarithmic Scales One or both axes Used to display data with large range of values Used to make some functional relationships more apparent, e.g. y = 10 (2x+3) is a straight line on a semilog plot Can use line specifiers and property-name property-value pairs as in plot On logarithmic axis, make sure all data is > 0 because otherwise log is undefined 28 14

15 MATLAB commands for log plots y = logspace(a,b,n) generates a row vector y of n points between decades 10 a and 10 b. If n omitted, default to 50 points y = logspace(a,pi) generates the points between 10 a and pi, which is useful for digital signal processing where frequencies over this interval go around the unit circle