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# ch02 - Attia John Okyere Plotting Commands Electronics and...

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Attia, John Okyere. “Plotting Commands.” Electronics and Circuit Analysis using MATLAB. Ed. John Okyere Attia Boca Raton: CRC Press LLC, 1999 © 1999 by CRC PRESS LLC

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CHAPTER TWO PLOTTING COMMANDS 2.1 GRAPH FUNCTIONS MATLAB has built-in functions that allow one to generate bar charts, x-y, polar, contour and 3-D plots, and bar charts. MATLAB also allows one to give titles to graphs, label the x- and y-axes, and add a grid to graphs. In addition, there are commands for controlling the screen and scaling. Table 2.1 shows a list of MATLAB built-in graph functions. One can use MATLAB’s help facility to get more information on the graph functions. Table 2.1 Plotting Functions FUNCTION DESRIPTION axis freezes the axis limits bar plots bar chart contour performs contour plots ginput puts cross-hair input from mouse grid adds grid to a plot gtext does mouse positioned text histogram gives histogram bar graph hold holds plot (for overlaying other plots) loglog does log versus log plot mesh performs 3-D mesh plot meshdom domain for 3-D mesh plot pause wait between plots plot performs linear x-y plot polar performs polar plot semilogx does semilog x-y plot (x-axis logarithmic) semilogy does semilog x-y plot (y-axis logarithmic) shg shows graph screen stairs performs stair-step graph text positions text at a specified location on graph title used to put title on graph xlabel labels x-axis ylabel labels y-axis © 1999 CRC Press LLC
2.2 X-Y PLOTS AND ANNOTATIONS The plot command generates a linear x-y plot. There are three variations of the plot command. (a) plot(x) (b) plot(x, y) (c) plot(x1, y1, x2, y2, x3, y3, ..., xn, yn) If x is a vector, the command plot(x) will produce a linear plot of the elements in the vector x as a function of the index of the elements in x. MATLAB will connect the points by straight lines. If x is a matrix, each column will be plotted as a separate curve on the same graph. For example, if x = [ 0 3.7 6.1 6.4 5.8 3.9 ]; then, plot(x) results in the graph shown in Figure 2.1 . If x and y are vectors of the same length, then the command plot(x, y) plots the elements of x (x-axis) versus the elements of y (y-axis). For example, the MATLAB commands t = 0:0.5:4; y = 6*exp(-2*t); plot(t,y) will plot the function y t e t ( ) = 6 2 at the following times: 0, 0.5, 1.0, …, 4 . The plot is shown in Figure 2.2 . To plot multiple curves on a single graph, one can use the plot command with multiple arguments, such as plot(x1, y1, x2, y2, x3, y3, ..., xn, yn) © 1999 CRC Press LLC

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Figure 2.1 Graph of a Row Vector x The variables x1, y1, x2, y2, etc., are pairs of vector. Each x-y pair is graphed, generating multiple lines on the plot. The above plot command allows vectors of different lengths to be displayed on the same graph. MATLAB automatically scales the plots. Also, the plot remains as the current plot until another plot is generated; in which case, the old plot is erased. The hold command holds the current plot on the screen, and inhibits erasure and rescaling. Subsequent plot commands will overplot on the original curves.
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ch02 - Attia John Okyere Plotting Commands Electronics and...

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