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15.1: scatter, scatter3

  • Page ID
    85204
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    The plot() and scatter() functions can make similar 2D plots

    Example \(\PageIndex{1}\) 2D plot() and scatter()

    %% Create random x and y data points
    n = 20;
    x = rand(1, n); % a 1xn vector of random values between 0 and 1
    y = rand(1, n); % another 1xn vector of random values between 0 and 1

    Compare the results of these codes.

    %% Plot with the plot function, open circlesplot2D_1.png
    figure;
    plot(x, y,'o')
    grid on

    Figure \(\PageIndex{1}\): plot(x, y,'o')

    %% Plot with the scatter function, open circlesscatter2D_1.png
    figure;
    scatter(x, y)
    grid on

    Figure \(\PageIndex{2}\): scatter(x, y)

    The markers can be filled in and the size changed with both plot() and scatter(), but the options are specified differently:

    %% Plot with the plot function, large, filled circlesplot2D_2.png
    figure;
    plot(x, y, 'o', 'MarkerFaceColor', 'g', 'MarkerSize', 20)
    title('plot(x, y,''o'', ''MarkerFaceColor'', ''g'', ''MarkerSize'', 20)')

    Figure \(\PageIndex{3}\): plot() with MarkerFaceColor and MarkerSize options

    %% Plot with the scatter function, large, filled circlesscatter2D_2.png

    figure;
    scatter(x, y, 200, 'filled') % size = 20, filled markers
    title('scatter(x, y, 200, ''filled'')')

    Figure \(\PageIndex{4}\): scatter() with size and 'filled' options

    Solution

    Add example text here.

    .

    Example \(\PageIndex{2}\) xlim, ylim, text

    This shows the use of the xlim() and ylim() functions with a 2D plot of a curve. It also shows how to use the text() function to add information to a figure. The code is attached in the file xlim_ylim_example.m

    %% Example for xlim, ylim, axis
    format short g; format compact; close all; clear all; clc;
    x = -6:0.1:6;
    y = -1 -5*x -0*x.^2 +0.3*x.^3;
    figure;
    plot(x,y, 'LineWidth',4);
    grid on;
    title('y = -1 -5*x -0*x^2 +0.3*x^3')

    %% Zoom in on x
    xlim([-3, 4]) % [x_lower_limit, x_upper_limit]

    %% Zoom out in y
    ylim([-1, 1]*12) % [y_lower_limit, y_upper_limit]

    %% Look for the zero crossing by zooming in on both x & y in 1 command
    axis([-1 1 -1 1]*0.5)
    % [x_low, x_up, y_low, y_up, ]
    % y = 0 at about x = -0.2

    %% Check
    y_len = length(x) % 121
    y(51:60)
    % W can see the the closest value to 0 is:
    y(59) % -0.0024
    % The corresponding x value is:
    x(59) % -0.2
    axis([-0.3 0.1 -.1 .1]) % zoom in

    %% text() example
    axis auto % reset the axes to their original scaling
    axis('auto')
    text(x(59), 0, ['a zero near ',num2str(x(59))])

    %% We see that the text is ovelapping with the curve.
    % So replot the curve on a new figure and raise the position of the text.

    figure;
    plot(x,y,'g','LineWidth',2);
    grid on;
    title('y = -1 -5*x -0*x.^2 +0.3*x.^3')
    text(x(59), 2.0, ['a zero near x= ',num2str(x(59))])

    %% Put texts near the other zeros
    text(-4, 10, ['a zero near x= ',num2str(-4)])
    text(4.2, -5, ['a zero near'])
    text(4.2, -8, ['x= +4'])

    %% Plot arrows pointing to the zeros
    hold on;
    quiver(-4,10, 0,-10, 'LineWidth',2)
    %quiver(x,y, dx,dy)
    quiver(4.2,-5, 0,5, 'LineWidth',2)
    %quiver(x,y, dx,dy)

    Solution

    Add example text here.

    .

    Exercise \(\PageIndex{1}\) xlim, ylim assignment

    A. Open a new figure and plot these 2 functions on it:
    x = (0:0.05:1)*pi;
    y1 = 0.3*x;
    y2 = cos(2*x);
    figure(1)
    plot(x,y1)
    hold on;
    plot(x,y2)
    grid on;

    We can see that these functions intersect near x = 0.7 and y = 0.2

    B. Use xlim, ylim to zoom in on the area near (0.7, 0.2).
    Set the x-limits to be [0.5, 1.0]
    Set the y-limits to be [0.1, 0.3]

    Save the figure and submit it.

    The figure can be saved in 2 ways:

    1. Under the File menu, select "Save as" and file type *.png or *.jpg and give it a file name.

    2. Under the Edit menu, select "Copy Figure", then paste it into a file. This is convenient when writing a report with multiple figures.

    Answer

    The answer is not given here.

    .

    The scatter3() function makes 3D plots

    Example \(\PageIndex{3}\) sphere with scatter3()

    %% scatter_plots_sphere.m
    format compact; format short; clear all; clc; close all;
    % scatter3() can plot data that is not on a rectangular grid.

    %% This example is adapted from Matlab's scatter help page.
    % sphere() is a built-in example
    [X,Y,Z] = sphere(16); % 17 x 17 grid
    X1D = X(:); % Convert X from a 17x17 array to a 289x1 vector
    Y1D = Y(:); % Convert Y from a 17x17 array to a 289x1 vector
    Z1D = Z(:); % Convert Z from a 17x17 array to a 289x1 vector

    %% Use scatter3() to create 3D plots.sphere1.png
    figure
    scatter3(X1D, Y1D, Z1D,'go','filled')
    % 'go' = green circles for the data markers
    % 'filled' = fills-in the circles
    title('3D scatter plot example: sphere')
    xlabel('X')
    ylabel('Y')
    zlabel('Z')
    axis equal

    %% The view angle can be changedsphere2.png
    [az, el] = view % This is the current view angle
    % az = -37.5000
    % el = 30
    view(45,10) % view(azimuth, elevation)

    %% Try adjusting the axis limits by evaluating each of these lines, 1 at a time.
    xlim([-2,2])
    ylim([0,1])
    zlim([0,1])
    xlim([-1,1])
    view(70,30)
    view(10,10)

    Solution

    Add example text here.

    ..

    Next we make a 3-dimensional scatter3() plot.

    Example \(\PageIndex{4}\) scatter3 helix

    %% scatter3D_helix.m
    format short g; format compact; clear all; close all; clc;
    %% The scatter3() function makes a 3D plot of individual points
    % The inputs to the scatter3() function are x, y, and z vectors defining each point.
    % Unlike other 3D plotting functions, it does not use a 2D grid of x and y coordinates

    % Define these x and y vectors:scatter3_helix.png
    r = 2; % radius of the helix
    ang = 0 : 10 : 3*360; % angles (degs)
    x = r*cosd(ang);
    y = r*sind(ang);
    n = length(ang);
    z = (0 : (n-1)) /8;

    %% Open a figure and plot this surface using the scatter3() function
    % scatter3 expects the 3 inputs to be vectors.
    figure;
    scatter3(x, y, z);
    axis equal

    %%
    title('scatter3() of a helix');
    xlabel('x') % This identifies x-axis
    ylabel('y')
    zlabel('z')
    % You can rotate the graph in 3D.
    % You can zoom in.

    Solution

    Add example text here.

    .

    Exercise \(\PageIndex{2}\) scatter3 for an undersea mountain

    The file scatter3_seamount_start.m code loads the seamount.mat data file. The seamount.mat file is attached to this section. You need to download it. The scatter3_seamount_start.m file and the seamount.mat both need to be in the same directory as the command window.

    You need to add the scatter() function to plot the x, y coordinates and the scatter3() function to plot the full 3D seamount. Change the name of the completed .m file scatter3_seamount_YourName.m

    Answer

    The answer is not given here.

    .


    This page titled 15.1: scatter, scatter3 is shared under a CC BY-NC-SA 4.0 license and was authored, remixed, and/or curated by Carey Smith.