learningMatlab

Plotting data

Let’s write a script to do the following things in sequence (include comments at each step!):

• create a variable n with a value of 20
• a vector t containing 1 to n (in steps of 1)
• a vector sig that is equal to 0.3 times the square of t
• use figure to pop up a new figure window
• use plot() to plot sig as a function of t
• Use a semicolon (;) to end each line (to suppress unwanted output)

>> doc plot  % if in doubt check help

more plotting…

There are many plotting / graphing related functions. Briefly play around with the following:

• xlabel() , ylabel() , title()

• you can provide string to them in single quotes ‘like this’. The single quotes are the way to define character strings. Ultimately, they can of course also be stored in variables.

• You can specify the linestyle and symbols for the plot easily:

  plot(t, sig, 'rs-' ) % red, square symbols, solid line
  

• There is also a way to create two plots on the same axes at the same time:

  plot(t, sig, 'rs-', t, sig./2, 'b:' )
  

The plot command is very versatile and you’ll see people use it in many different ways. If you read the help/documentation for the command you’ll see that the first/normal use is to provide both x and y coordinates for the points you want to plot, e.g.:

x = 1:10;
y = rand(1,10); % 10 random numbers
plot(x,y) % simple plot
plot(x,y, 'rs--') % plot with line style
%
y2 = rand(1,10); % another 10 numbers
plot(x,y, 'rs--', x,y2, 'bo-') % two plots in one

Function exercises

• Write a function myPlot() that takes two input arguments and returns no output argument. All the function should do is to use the matlab plot() command as per usual, but with your preferred properties for the plot. Look at help plot to get some inspiration, but inside your function you might want to try to use, e.g. the properties

'linewidth', 2   % or whichever thickness you like
'color', [1 1 0] % or some other color triplet in red, green, blue
'markersize', 15
'marker', 's'

Next

Loops, if/else, controlling flow - loops and controls

This site is open source. Improve this page.