CSE 123

Plots in MATLAB

Easiest way to plot

Syntax: ezplot(fun)

ezplot(fun,[min,max])

ezplot(fun2)

ezplot(fun2,[xmin,xmax,ymin,ymax])

ezplot(fun) plots the expression fun(x) over the default domain -2pi < x < 2pi.

ezplot(fun,[min,max]) plots fun(x) over the domain: min < x < max.

ezplot(fun2) plots fun2(x,y)= 0 over the default domain -2pi < x <2pi, -2pi < y < 2pi.

Example:

>>ezplot('x^3-2*x')

-6 -4 -2 0 2 4 6-250

-200

-150

-100

-50

0

50

100

150

200

250

x

x3-2 x

>> ezplot('x^3-x',[-5 5])

-5 -4 -3 -2 -1 0 1 2 3 4 5-150

-100

-50

0

50

100

150

>> ezplot('x^2-y^4‘[-5,5,-4,4])

-5 -4 -3 -2 -1 0 1 2 3 4 5-4

-3

-2

-1

0

1

2

3

4

x

y

x2-y4 = 0

plot command: Linear 2-D plot

 Syntax: plot(X,Y,linespec, ‘PropertyName',PropertyValue, …)

LineWidth - specifies the width (in points) of the line.

MarkerEdgeColor - specifies the color of the marker or the edge color for filled markers (circle, square, diamond, pentagram, hexagram, and the four triangles).

MarkerFaceColor - specifies the color of the face of filled markers.

MarkerSize - specifies the size of the marker in units of points.

Examples:

x=1:50;y=sin(x*pi/10)+cos(x*pi/10);plot(x,y)

plot(x,y,'--ro')

Examples:

0 5 10 15 20 25 30 35 40 45 50-1.5

-1

-0.5

0

0.5

1

1.5

0 5 10 15 20 25 30 35 40 45 50-1.5

-1

-0.5

0

0.5

1

1.5

0 5 10 15 20 25 30 35 40 45 50-1.5

-1

-0.5

0

0.5

1

1.5

0 5 10 15 20 25 30 35 40 45 50-1.5

-1

-0.5

0

0.5

1

1.5

Example

plot(x,y,'-kd', 'MarkerEdgeColor',‘g', 'MarkerFaceColor', ‘r' )

plot(x,y,'-k', 'Linewidth', 5 )

Example

0 5 10 15 20 25 30 35 40 45 50-1.5

-1

-0.5

0

0.5

1

1.5

0 5 10 15 20 25 30 35 40 45 50-1.5

-1

-0.5

0

0.5

1

1.5

Plotting multiple plots on the same figure

x=1:50;y1=cos(x*pi/10); y2=sin(x*pi/10);plot(x,y1,x,y2)

0 5 10 15 20 25 30 35 40 45 50-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

x=1:50;y1=cos(x*pi/10); y2=sin(x*pi/10);plot(x,y1)hold onplot(x,y2)

0 5 10 15 20 25 30 35 40 45 50-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

Plotting multiple plots on the same figure

plot(x,y1,’k’,x,y2,’r’)

x=1:50;y1=cos(x*pi/10); y2=sin(x*pi/10);

plot(x,y1,’k’)hold onplot(x,y2,’r’ )

Editing plots with editplot

Syntax plotedit on plotedit off

2 plots: one above the other = 2-by-1 matrix

4 plots: in a 2x2 array = 2-by-2 matrix

subplot command

Syntax: subplot(N,M,i)

Notes: *This function does NOT create a plot *It HAS to be used BEFORE the plot function !!!!

N= number of rowsM= number of columnsi= current plot number

Subplot(2,1,1)

Subplot(2,1,2)

(2,2,1) (2,2,2)

(2,2,3) (2,2,4)

Plotting multiple plots on the same figure

x=1:50;y1=cos(x*pi/10);y2=1000*y1;

plot(x,y1,x,y2,’k’); grid on

subplot(2,1,1)plot(x,y1); grid onsubplot(2,1,2)plot(x,y2,’k’); grid on

Plot features: xlabel, ylabel, title, grid

x=1:50;y1=cos(x*pi/10); y2=sin(x*pi/10);

plot(x,y1,x,y2)xlabel(‘x’); ylabel(‘y’);title(‘Example’)grid on

text(15,0.8,’y1’)text(20,-0.2,’y2’)

Plot features: text and legend

legend(‘y1’,’y2’)

plotyy 2-D line plots with y-axes on both left and right side

Syntax plotyy(X1,Y1,X2,Y2)

plotyy(X1,Y1,X2,Y2) plots X1 versus Y1 with y-axis labeling on the left and plots X2 versus Y2 with y-axis labeling on the right.

Example:

>>x=0:0.05:5;y=sin(x.^2);z=cos(x.^2);plotyy(x,y,x,z)

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5-1

-0.5

0

0.5

1

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5-1

-0.5

0

0.5

1

%% Line Plot of a Chirpx=0:0.05:5;y=sin(x.^2);plot(x,y);

>> %% Bar Plot of a Bell Shaped Curvex = -2.9:0.2:2.9;bar(x,exp(-x.*x));

>> %% Bar Plot of a Bell Shaped Curvex = -2.9:0.2:2.9;bar(x,exp(-x.*x));

>> %% Stairstep Plot of a Sine Wavex=0:0.25:10;stairs(x,sin(x));

>> %% Errorbar Plotx=-2:0.1:2;y=erf(x);e = rand(size(x))/10;errorbar(x,y,e);

>> % Polar Plott=0:.01:2*pi;polar(t,abs(sin(2*t).*cos(2*t)));

>> x = 0:0.1:4;y = sin(x.^2).*exp(-x);stem(x,y)

Logarithmic Plots

commands

semilogx() plots x data on log axis and y on linear axis

semilogy() plots y data on log axis and x on linear axis

loglog() plots x and y on logarithmic axes

Logarithmic Plots

Example: plot y=e2x

>> x=0:0.1:10;>> y=exp(2.*x);>>plot(x,y)>> semilogy(x,y)

0 1 2 3 4 5 6 7 8 9 100

0.5

1

1.5

2

2.5x 10

4

0 1 2 3 4 5 6 7 8 9 1010

0

101

102

103

104

105

Three dimensional plots

Three dimensional line plots the simplest form is

plot(x,y,z) x,y,z are arrays of equal size containing the locations of data points to plot.

Example: x(t)= e-0.2tcos (2t)

y(t)= e-0.2tsin(2t) motion of an insect

t=0:0.1:10;x=exp(-0.2*t).*cos(2*t);y=exp(-0.2*t).*sin(2*t);plot(x,y)title('\bf 2D plot')xlabel('\bfx')ylabel('\bfy')grid on

Three dimensional plots

instead we could plot the variables with plot3() to preserve the time information as well as the 2D position of the object.

plot3(x,y,t)

t=0:0.1:10;x=exp(-0.2*t).*cos(2*t);y=exp(-0.2*t).*sin(2*t);plot3(x,y,t)title('\bf 3D plot')xlabel('\bfx')ylabel('\bfy')zlabel('\bftime')grid on

Three dimensional plots

surface, Mesh and contour plots: such kind of plots represent data that is a function of 2D variables. a user must create three arrays of equal size;

Commands:mesh(x,y,z) creates a mesh or wireframe plot where x,y and z are 2D

arrays of containing x,y,z values at every point, respectively.surf(x,y,z) creates a surface plot,contour(x,y,z) creates a contour plot,

[x,y]=meshgrid(xstart:xinc:xend, ystart:yinc:yend) easily create x and y arrays required for 3D plots

to create a 3D plot use meshgrid to create the arrays of x and y values then evaluate the function to plot at each of x,y pairs. finally call the above mentioned functions to create plot.

Three dimensional plots

Example:create the mesh plot of the following function

])(5.0[5.0 22

),( yxxeyxz

over the interval 4444 yandx

[x,y]=meshgrid(-4:0.1:4);

z= exp(-0.5*(x.^2+0.5*(x-y).^2));

mesh(x,y,z);