Matlab_09a

Functions

We are now going to create a few functions.

To make the first example easy I supply the text for you to copy and paste below. Select

File -> New -> M File 

to create a blank page and paste in this text:

function cost_to_destination = mypetrolcost(distance_to_destination)

% this is the function equivalent of the 

% calculation we explored in matlab_03

%

cost_per_litre = 1.1;

miles_per_litre = 5;

cost_to_destination  = distance_to_destination  / miles_per_litre * cost_per_litre;

end

Save the file and give it *exactly the same name as the function*! This file must be called mypetrolcost.m or there will be loads of problems later.

Your function can now be executed from the command line like this:

>> mypetrolcost(100)

ans =

    22

Notice that by creating and saving a function we have extended the language of Matlab - we have used Matlab to write a new capability for Matlab.

Here is another example we have seen from an earlier exercise.

To make this easy I also supply the text for you to copy and paste below. Select

File -> New -> M File 

to create a blank page and paste in this text:

function r = mygraph(x)

y_1 = x.*x;        % this gives us x squared

y_2 = x.*x.*x;     % this gives us x cubed

plot(x,y_1,'r');   % plot the x squared graph

hold on;           % hold the plot for a second line

plot(x,y_2,'g');   % plot x cubed

%

% some extra things added to the graph

xlabel('x values');

ylabel('y values');

title('my first graph')

legend({'x^2' 'x^3'});

grid on;

end

Save the file and give it *exactly the same name as the function*! This file must be called mygraph.m

Your function can now be executed from the command line like this:

>> mygraph(100:1:200)