Polar Graphs in Octave

In this lesson, I'll show you how to draw a polar graph in Octave.

What is a polar graph? A polar graph (or polar plot) is a circular graph used in scientific contexts to represent the polar coordinates of a function.

Let me give you a practical example.

Create the vector theta of angular variations.

>> theta = 0 : 0.1 : 2*pi;

This command creates a vector containing values from 0 to 2π (360°) with a constant increment of 0.1.

Now, define an array with the values of the function as a function of the angular variations theta.

>> y1=0.5+(1.3).^(theta);

The arrays theta and y1 have the same number of elements.

To represent the function on a polar graph, use the function polar()

>> PolarGraph = polar(theta,y1,"*");

Octave displays the polar graph, and each point is indicated with an asterisk.

In this case, it is a spiral function.

How to draw two functions overlapping on the polar graph?

First, clear the screen from the previous example.

clf

Create the vector of angular variations again.

>> theta = 0 : 0.1 : 2*pi;

Now, generate the arrays of two functions y1 and y2 instead of one.

>> y1=0.5+(1.3).^(theta);
>> y2 = 3*(1 - cos(theta));

Next, create a matrix [m] that contains both functions.

>> m = [y1;y2];

This way, you can display both functions overlapping on the graph using the polar() function only once.

>> PolarGraph = polar(theta,m);

Both functions are printed on the polar graph.

However, the two lines are difficult to see.

To double the thickness of the lines, use the set() command.

set(PolarGraph,"LineWidth",2);

Now the multiple polar graph is certainly more understandable.

To add a legend to the graph, use the legend() function.

legend("y1","y2");

The legend appears near the polar graph in the top right corner.

This way, you can represent two or more overlapping functions in a single polar graph.

Note.For example, create a new function y3, generate a matrix with three functions m = [y1; y2; y3]. Then, display the three graphs on the polar graph.

Now the polar graph displays three overlapping functions.

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