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ENGR 1181 | MATLAB 13: 2D Plots 2 Preparation Material Learning Objectives 1. Create other 2D graphing options in MATLAB (e.g., log, bar, subplot, fplot) 2. Select the proper opportunities to utilize aforementioned 2D graphing options Topics Students will read Chapter 5 of the MATLAB book before coming to class. This preparation material is provided to supplement this reading. Students will learn more advanced techniques and syntax for creating and formatting twodimensional (2D) plots in MATALB. This material contains the following: 1. 2. 3. 4. Organize Multiple Plots on the Same Page Logarithmic Plots Plots with Special Formats The fplot() Command 1. Organize Multiple Plots on the Same Page Multiple plots on one page can be created with the subplot() command. subplot(m, n, p) This command creates mxn plots in the Figure Window. The plots are arranged in m rows and n columns. The variable p defines which plot is active. The plots are numbered from 1 to mxn. The upper left plot is 1 and the lower right plot is mxn. The numbers increase from left to right within a row, from the first row to the last. For example, to create 6 plots arrange in 3 rows and 2 columns, enter the following: 1 ENGR 1181 MATLAB 13: 2D Plots 2 Preparation Material subplot(3, 2, p) 2 ENGR 1181 MATLAB 13: 2D Plots 2 Preparation Material The following script files is used to execute the plots from the previous page: 3 ENGR 1181 MATLAB 13: 2D Plots 2 Preparation Material 2. Logarithmic Plots The following commands are used to plot with logarithmic scales (axes): Important Facts about Logarithmic Plots Remember the following about logarithmic plots: 1. Negative numbers cannot be plotted on log scales (because the log of a negative number is not defined). 2. The number zero (0) cannot be plotted on a log scale. 3. The tick-mark labels on a log scale are the actual values being plotted (they are not the logarithms of the numbers). 4. Equal distances on a log scale correspond to multiplication by the same constant (as opposed to a linear scale, where equal distances correspond to the addition of the same constant). 5. Tick marks are not evenly spaced. 4 ENGR 1181 MATLAB 13: 2D Plots 2 Preparation Material Plotting with Linear and Log Scales Plots can look very different based on scale of numbers, but also on the type of scale. The following shows the variation of graphs for the formula: y 81 x 5 ENGR 1181 MATLAB 13: 2D Plots 2 Preparation Material 3. Plots with Special Formats The following commands are used for plots with special geometry: bar(x,y) Creates a bar chart of y vs. x. stairs(x,y) Creates a stairs chart of y vs. x. stem(x,y) Creates a stem chart of y vs. x. polar(theta,r) Creates a polar plot. The vectors theta and r contain the polar coordinates and r, respectively. Below are examples of each of these type of plot formats: 30 30 25 20 Sales (million $) Sales (million $) 25 15 10 20 15 10 5 0 1988 1990 1992 Year 5 1988 1994 1989 1990 1991 Year 1992 1993 1994 stairs(x,y) bar(x,y) 30 90 20 120 60 25 10 Sales (million $) 150 30 20 180 15 0 10 210 330 5 240 0 1988 300 270 1989 1990 1991 Year 1992 stem(x,y) 1993 1994 polar(theta,radius) 6 ENGR 1181 MATLAB 13: 2D Plots 2 Preparation Material 4. The fplot() Command The fplot() command can be used to plot a function with the form: y = f(x) fplot(‘function’,limits) Remember the following about the fplot() command: The function is typed in as a string. The limits is a vector with the domain of x, and optionally with limits of the y axis: [ xmin , xmax ] or [ xmin , xmax , ymin , ymax ] Line specifiers can be added, just like with plot command Plotting with the fplot() Command For example, let’s say we want to plot the following equation and domain: y x 2 4 sin( 2 x) 1 for 3 x 3 The MATLAB syntax would be the following equation and the output is below: >> fplot('x^2 + 4 * sin(2*x) - 1', [-3 3]) 7