5.4: Line Plotting

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Masayuki Yano, James Douglass Penn, George Konidaris, & Anthony T Patera
Massachusetts Institute of Technology via MIT OpenCourseWare

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We include line plotting in this chapter as we now have the necessary pieces: single-index arrays, and characters. We do not present all the various options since these can readily be found by >> help plot or the documentation. However, we do provide a template which you can use and adapt accordingly.

%A sample plotting script - by Justin Miller

%----------- linear-linear plotting, sine and cosines ---------------

L = 2*pi; %Define the ending angle

N = 100; %Define number of angle segments

xpts = (L/N)*[0:N]; %Define a set of angles for plotting (in radians)

%This could also be done using

%xpts = linspace(0,L,N+1);

sin_values = sin(xpts); %Sine vector of each angle

cos_values = cos(xpts); %Cosine vector of each angle

figure %Create a figure window to draw the plots

plot(xpts,sin_values,'b-') %Plot the sine values in a blue line

hold on %Hold the current figure when plotting

%the next figure

plot(xpts,cos_values,'r--') %Plot the cosine values in a red dashed line

h_sincos_plot = gcf; %Get the handle of the current figure

ha_sincos_axis = gca; %Get the handle of the current axis

axis([0,xpts(end),-1.1,1.1]) %Set the x and y axes [xmin,xmax,ymin,ymax]

set(ha_sincos_axis,'XTick',0:pi/2:2*pi) %Set the location of the x tick marks

set(ha_sincos_axis,'YTick',-1:0.2:1) %Set the location of the y tick marks

set(ha_sincos_axis,'XTickLabel',{'0','pi/2','pi','3*pi/2','2*pi'})

%Set the names of each x tick mark

xlabel('Angle (radians)') %Give a label name to the x axis

ylabel('Trigonomic output') %Give a label name to the y axis

title(['Plot of sin and cos from x = ',num2str(xpts(1)), ...

' to x = ',num2str(xpts(end))])

%Give the figure a title

legend('sin','cos','location','best') %Provide a legend and tell matlab to place

%it in the best location

saveas(h_sincos_plot,'sin_cos.fig') %Take the figure specified by handle

%"h_sincos_plot" and save it

%as "sin_cos.fig" in the working directory

%----------- log-linear plotting, exponential ---------------

clear all

L = 5;

N = 100;

x = (L/N)*[0:N];

y = 2*exp(x);

figure

semilogy(x,y,'b-') %Create a plot where only the y axis is in log scale

%semilogx would plot only the x axis in log scale

xlabel('x')

ylabel('y')

title(['Log-Linear plot of y = 2*exp(x) from x = ',num2str(x(1)), ...

' to x = ',num2str(x(end))])

saveas(gcf,'exp.fig')

%----------- log-log plotting, polynomials ---------------

clear all

L = 10^2;

N = 100;

x= (L/N)*[0:N];

y = 2*(x.^3);

figure

loglog(x,y,'b-') %Create a plot where both axes are in log scale

xlabel('x')

ylabel('y')

title(['Log-Log plot of y = 2x^3 from x = ',num2str(x(1)), ...

' to x = ',num2str(x(end))])

saveas(gcf,'poly.fig')

MATLAB also has extensive "3-D" plotting capabilities.