Functions

Funk-shuns?

+

Dys-function?

Dat-function?

No! We want...

...a named procedure that performs a distinct service

Anatomy of a function

Function Naming

The name of your first function must be the name of the file!

iAm.m function x = iAm(yes,it,is,true)
iAmNot.m function x = iAm(no,it,is,false)
usage with unmatching names iAmNot(no,it,is,false)

To avoid confusion, use the same name for both the function file and the first function within the file. MATLAB associates your program with the file name, not the function name. Script files cannot have the same name as a function in the file.


You need to save your file in the same location you expect to use it.

Functions with no input, no output

If you have no input values and no output values:

function myFunction

function plotSinx
% usage: plotSinx
% This function plots sin(x) from 0 to 2*pi
% there are no inputs or outputs (other than the plot itself)

% set the fixed domain
x = linspace(0,2*pi);

% define the sin function
f = sin(x);

% and plot
plot(x,f)
plotSinx.m

Ask user for input after function starts running

function plotSin2
% usage: plotSin2
% This function plots sin(x) over a domain specified by user
% We will query the user for input values then display a plot of sin(x)
% over that domain

% get starting and ending
disp('You will define the plotting domain for sin(x).');
l = input('Enter the starting x value:');
h = input('Enter the ending x value:');

x = linspace(l,h);

% define the sin function
f = sin(x);

% and plot
plot(x,f)
plotSin2.m

Functions with input, no output

If you have input values but no output values:

function myFunction(x)

function [ ] = myFunction(x)

function plotSin3(x)
% usage: plotSin3(x) where x is a vector
% This function plots sin(x) over a domain, x, specified by user

% define the sin function
f = sin(x);

% and plot
plot(x,f)
plotSin3.m

If you have multiple input values and no output values:

function myFunction(x,y,z)

function [ ] = myFunction(x,y,z)

function plotSin4(a,b,n)
% usage: plotSin4(a,b,n)
% a = starting x value
% b = ending x value
% n = number of segments between a and b

% define the domain from input values
x = linspace(a,b,n);

% define the sin function
f = sin(x);

% and plot
plot(x,f)
plotSin4.m

Functions with no input, output

If you have no input values but have output values:

function a = myFunction

function [a,b,c] = myFunction

function x = createRandInt
% generate a pseudo-random number

a = clock;

x = round(a(6));
createRand.m

Functions with input, output

If you have no input values but have output values:

function a = myFunction(x,y,z)

function [a,b,c] = myFunction(x,y,z)

function [r,theta] = cart2plr(x,y)
% Convert Cartesian coordinates to polar coordinates
% usage: [r,theta] = cart2plr(x,y) computes r and theta
% from x and y values (arrays are allowed)
% r = sqrt(x^2 + y^2);
% theta = atan2(y,x);

r = sqrt(x^2 + y^2);
theta = atan2(y,x);
cart2plr.m

Functions in Scripts

Call a Function

% This script will call a function to calculate the area and circumference
% of a circle. User will supply the radius.

clear all
clc

disp('We will find the area and circumference of any circle!');
r = input('What is the radius of your circle? ');

% call our function that returns area and circumference
[a,c] = circleData(r);

fprintf('\nThe area of your circle is %.2f square units.\n\n',a);
fprintf('The circumference of your circle is %.2f units.\n\n',c);
scriptFn.m

Local Functions (R2016b and later)

% This script will call a function to calculate the area % and circumference
% of a circle. User will supply the radius.

clear all
clc

disp('We will find the area and circumference of any circle!');
r = input('What is the radius of your circle? ');

% call our function that returns area and circumference
[a,c] = circleData(r);

fprintf('\nThe area of your circle is %.2f square units.\n\n',a);
fprintf('The circumference of your circle is %.2f units.\n\n',c);
function [a,c] = circleData(r)
% return the area and circumference of a circle of any radius
% usage: [a,c] = circleData(r) where r is the radius of the circle

area = areaCalc(r);
circum = circumCalc(r);

% nested function to handle the area calculation
function y = areaCalc(s)
y = pi*s^2;
end

% nested function to handle the circumference calculation
function z = circumCalc(t)
z = 2*pi*t;
end

end
scriptFn2.m

Nested Functions



function [a,c] = circleData(r)
% return the area and circumference of a circle of any radius
% usage: [area,circum] = circleData(r) where r is the radius of the circle

area = areaCalc(r);
circum = circumCalc(r);

% nested function to handle the area calculation
function y = areaCalc(s)
y = pi*s^2;
end

% nested function to handle the circumference calculation
function z = circumCalc(t)
z = 2*pi*t;
end

end
circleData.m

Recursive Functions



function result=recursiveFn(x)
% usage: recursiveFn(num) where num is a positive integer
% This function computes the factorial of any positive integer

if (x<=0)
   result=1;
else
   result=x*recursiveFn(x-1);
end

end
recursiveFn.m

Variable Scope



Variables defined in functions do not leave the function

function x = createRandInt
% generate a pseudo-random number

a = clock

x = round(a(6));
>> a

Algorism and Bushism of the Day

"It has come to my attention, that air pollution is polluting the air!"

"We can build a collective civic space large enough for all our separate identities, that we can be e pluribus unum -- out of one, many."

E Pluribus Unum is Latin for "out of many, one"

Lesson of the Day - Managing your thoughts

The average person has between 16,000 and 80,000 thoughts per day.


Up to 80% of those thoughts have a negative connotation.


98% are the same thoughts from yesterday.


Whether you think you can or think you can't, you're right.


Don't believe everything you think.



Word of the day

RUN

DMC



The End