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MATLAB课程：代码示例之Graphics and Visualization（四）
Visualizing Four-Dimensional Data
This example shows several techniques to visualize four dimensional (4-D) data in MATLAB®.
Visualize 4-D Data with One Discrete Variable
Sometimes data has a variable which is discrete with only a few possible values. You can create multiple plots of the same type for data in each discrete group. For example, use thestem3 function to see the relationship between three variables where the fourth variable divides the population into discrete groups.
load patients Smoker Age Weight Systolic % load datansIdx = Smoker == 0;smIdx = Smoker == 1;figurestem3(Age(nsIdx), Weight(nsIdx), Systolic(nsIdx), 'Color', 'b') % stem plot for non-smokershold onstem3(Age(smIdx), Weight(smIdx), Systolic(smIdx), 'Color', 'r') % stem plot for smokershold offview(-60,15)zlim([100 140])xlabel('Age') % add labels and a legendylabel('Weight')zlabel('Systolic Blood Pressure')legend('Non-Smoker', 'Smoker', 'Location', 'NorthWest')
With a large data set you might want to see if individual variables are correlated. You can use the plotmatrix function to create an n by n matrix of plots to see the pair-wise relationships between the variables. The plotmatrix function returns two outputs. The first output is a matrix of the line objects used in the scatter plots. The second is a matrix of the axes objects that are created.
The plotmatrix function can also be used for higher order data sets.
load patients Height Weight Diastolic Systolic % load datalabels = {'Height' 'Weight' 'Diastolic' 'Systolic'};data = [Height Weight Systolic Diastolic];[h,ax] = plotmatrix(data); % create a 4 x 4 matrix of plotsfor i = 1:4 % label the plots xlabel(ax(4,i), labels{i}) ylabel(ax(i,1), labels{i})end
For many kinds of four dimensional data, you can use color to represent the fourth dimension. This works well if you have a function of three variables.
For example, represent highway deaths in the United States as a function of longitude, latitude, and if the location is rural or urban. The x, y, and z values in the plot represent these three variables. The color represents the number of highway deaths.
claload accidents hwydata % load datalong = -hwydata(:,2); % longitude datalat = hwydata(:,3); % latitude datarural = 100 - hwydata(:,17); % percent rural datafatalities = hwydata(:,11); % fatalities datascatter3(long,lat,rural,40,fatalities,'filled') % draw the scatter plotax = gca;ax.XDir = 'reverse';view(-31,14)xlabel('W. Longitude')ylabel('N. Latitude')zlabel('% Rural Population')cb = colorbar; % create and label the colorbarcb.Label.String = 'Fatalities per 100M vehicle-miles';
Your data may contain a measured value for a physical object such as temperature in a pipe. In this cases, the physical dimensions can be represented as a volume with color used to represent the magnitude of the measurement. For example, use the slice function to show the value of the measured variable at cross-sections within the volume.
load fluidtemp x y z temp % load dataxslice = [5 9.9]; % define the cross sections to viewyslice = 3;zslice = ([-3 0]);slice(x, y, z, temp, xslice, yslice, zslice) % display the slicesylim([-3 3])view(-34,24)cb = colorbar; % create and label the colorbarcb.Label.String = 'Temperature, C';
A complex function has an input with real and imaginary parts and an output with real and imaginary parts. You can use a three dimensional plot with color to represent the complex function. In this case the x and y axes represent the real and imaginary parts of the input. The z axis represents the real part of the output and the color represents the imaginary part of the output.
r = (0:0.025:1)'; % create a matrix of complex inputstheta = pi*(-1:0.05:1);z = r*exp(1i*theta);w = z.^3; % calculate the complex outputssurf(real(z),imag(z),real(w),imag(w)) % visualize the complex function using surfxlabel('Real(z)')ylabel('Imag(z)')zlabel('Real(w)')cb = colorbar;cb.Label.String = 'Imag(w)';
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