Graphing

Line Plots

For this example we use one of Matlab's sample dataset to plot a simple line plot showing the time series movement of the stock market data. First Load the data.

load stockreturns

The data contains a (100x10) matrix of stock market observations and we are going to plot all of these data point on a single line plot using the plot function.

figure
plot(stocks(:))

To modify an existing plot use the hold on command. Subsequent plots will then be added to the current figure. For example to add to horizontal lines indicating +/- 1 standard deviation of the stocks data:

sd=std(stocks(:);
hold on
plot(xlim, [sd sd],'--r')
plot(xlim, [-sd -sd],'--r')

Here, in each case the plot function is plotting a straight line between two points. The first argument, xlim queries the figure to get the coordinates of the start and end of the x-axis (a two element vector), provides the x coordinates. The second argument is a vector containing the corresponding y coordinates of the two points.

The '--r' arguments specifies the plotted line to a red dashed line. Matlab supports a number of line (and marker) types of varying colours; for full details refer to Matlab's documentation on LineSpec.

Scatter Diagrams

figure
scatter(educ,wage)

gscatter(educ,wage,female,'rk','do')
xlabel('years of education')
ylabel('average hourly earnings')
legend('female','male','Location','northwest')

Histograms

hist(stocks(:))

figure
hist(stocks(:),40)
set(get(gca,'child'),'FaceColor','cyan','EdgeColor','blue');
title('Histogram of stock prices')

Distribution Plots

Theoretical Distributions

x=linspace(-5,5,1000);
xnorm = normpdf(x);
figure
plot(x,xnorm,'-k','LineWidth',2)
title('Probability density plot of standard Normal distribution')

hold all
df = [1,5,10];
for ii=1:length(df)
    xt = tpdf(x,df(ii));
    plot(x,xt)
end
title('Comparing t-distributions with standard Normal')
legend('Normal','T-dist df=1','T-dist df=5','T-dist df=10')