Plotting Error Bars in MATLAB

Error bars are a way of plotting errors on each point in a data set as vertical bars in a linear plot. MATLAB provides a simple function to plot the error bars for a given data; the errorbar() function.

Syntax:

errorbar(x,y,errors,…)

Where, 

• x – contains x data
• y- contains y data
• error – contains errors for every point in y with respect to x.

Now, let us see the same in implementation with some examples.

Let us create error bars of equal length first.

Example 1:

Matlab

% MATLAB code for Plot a graph
% X data
x = 0.1*[1:35];

% Y data
y = x.^2;
error = 3*ones(size(y));

% Defining error bars of same length
errorbar(x,y,error)

Output:

We can change the error bars from vertical to horizontal.

Example 2:

Matlab

% MATLAB code for plot error bar
% X data
x = 1:2:23;

% Y data
y = x.^2;

% Defining error bars of same length
error = 3*ones(size(y));
errorbar(x,y,error,'horizontal')

Output:

MATLAB allows us to print both vertical and horizontal error bars together, of the same length.

Example 3:

Matlab

x = 0.1*[1:2:23];    %xdata
y = x.^2;    %ydata
error = 0.23*ones(size(y));    %defining error bars of same length
errorbar(x,y,error,'both')

Output:

We can have variable lengths of error bars on either side of the y curve. See the following implementation for the same.

Example 4:

Matlab

x = [1 3 5.5 6 6.9 7.5 7.9];    %xdata
y = 0.003*x.^3;    %ydata

%defining error bars above the curve
error_pos = [1 0.5 1 0.2 0.3 0.23 0.7];

%defining error bars above the curve
error_neg = [0.7 0.23 0.3 0.2 1 0.5 1];
% first we pass the error below curve
% then, error above curve
errorbar(x,y,error_neg,error_pos)

Output:

We can plot both vertical and horizontal error bars of variable lengths.

Example 5:

Matlab

x = [1 3 5.5 6 6.9 7.5 7.9];    %xdata
y = 0.003*x.^3;    %ydata
y_error_pos = [1 0.5 1 0.2 0.3 0.23 0.7];    %defining y-error bars above the curve
y_error_neg = [0.7 0.23 0.3 0.2 1 0.5 1];   %defining y-error bars below the curve
x_error_pos = [0.7 0.23 0.3 0.2 1 0.5 1];   %defining x-error bars above the curve
x_error_neg = [1 0.5 1 0.2 0.3 0.23 0.7];   %defining x-error bars below the curve
%first the errors along y-axis are passed in order and then, that of x-axis
errorbar(x,y,y_error_neg,y_error_pos,x_error_neg,x_error_pos,'o')

Output:

The ‘o’ option plots a circle at (x, y) point instead of a continuous line.

We can also get the properties of the error bar created by making it an object like below:

Example 6:

Matlab

x = [1 3 5.5 6 6.9 7.5 7.9];    %xdata
y = 0.003*x.^3;    %ydata

%defining y-error bars above the curve
y_error_pos = [1 0.5 1 0.2 0.3 0.23 0.7];

 %defining y-error bars below the curve
y_error_neg = [0.7 0.23 0.3 0.2 1 0.5 1];

%defining x-error bars above the curve
x_error_pos = [0.7 0.23 0.3 0.2 1 0.5 1];

x_error_neg = [1 0.5 1 0.2 0.3 0.23 0.7];
err = errorbar(x,y,y_error_neg,y_error_pos,x_error_neg,x_error_pos,'o')
%creating an errorbar object

Output:

The plot would be:

And the properties will be displayed in the terminal.