MATLAB Functions: Definition, Syntax, Subfunctions, Anonymous Functions, Slides of Computer Programming

Download MATLAB Functions: Definition, Syntax, Subfunctions, Anonymous Functions and more Slides Computer Programming in PDF only on Docsity! Outline Functions M-files Subfunctions Anonymous functions Examples Factorial Function Approximating Sine function Sieve of Eratosthenes Lecture 05 Functions docsity.com Functions Syntax function [y1,..,yN] = func name(x1,..,xM) % Help text written here and it will be % shown until the first non−comment line % Do stuff end % optional Lecture 05 Functions docsity.com Variable Scope Function Scope function z = fname (x,y) % This file has to be named fname.m z = x + y; end Global Scope x = 5; disp(x); a = input('Enter x: '); b = input('Enter y: '); c = fname(a,b); disp(c); disp(x); Lecture 05 Functions docsity.com Subfunctions Functions within functions function y = myfunc(x) y = sub1(sqrt(x)) + sub2(x) function t = sub1(x) t = log(x); end function r = sub2(p) r = 2*p; end end Lecture 05 Functions docsity.com Anonymous Functions not stored in a file myfunc = @(x) (xˆ2); y = myfunc(3); Lecture 05 Functions docsity.com Primes Function Question What are all prime numbers ≤ N? Using what we know function p = primes1 (N) p = []; % creates an empty array for j = 1:N if isprime(j) % built−in isprime p = [p, j]; % expands the array end end end Lecture 05 Functions docsity.com A Better Primes Function Add knowledge All prime numbers, except 2, are odd numbers. Updated code function p = primes2 (N) if N>1, p = [2]; else p = []; end % check only odd numbers for j = 3:2:N if isprime(j) p = [p, j]; end end end Lecture 05 Functions docsity.com Measuring Performance tic/toc tic starts the timer, toc returns the elapsed time. Comparing primes functions N = input('Enter N: '); tic % Start timer p0 = primes(N); % Call built−in primes t0 = toc; % Stop timer and % store elapsed time % Let's also measure our functions tic; p1 = primes1(N); t1 = toc; tic; p2 = primes2(N); t2 = toc; Lecture 05 Functions docsity.com