 Math Review with Matlab: Calculus Taylors Series S. Awad, Ph.D. M. Corless, M.S.E.E. D. Cinpinski E.C.E. Department University of Michigan-Dearborn Calculus: Taylor Series Math Review with Matlab U of M-Dearborn ECE Department Series Operations Symbolic Summation Taylor Series Taylor Command

Taylor Series Example Approximation and Comparison Example 2 Calculus: Taylor Series Math Review with Matlab U of M-Dearborn ECE Department Symbolic Summation Find the sum of the following series s1 and s2 if they converges Example 1: 1 S1 2 x 1 x

Example 2 4x2 x 3 S 2 3 x 2x x 1 s1=symsum(1/x^2,1,inf) s1 = Converges 1/6*pi^2 num = 4*x*x-x-3 den = x^3+2*x s2=symsum(num/den,1,inf) s2 = Diverges! inf 3 Calculus: Taylor Series Math Review with Matlab

U of M-Dearborn ECE Department Summation Examples Example 3: s3=symsum(1/(x-1.5)^2,1,inf) s3 = 4+1/2*pi^2 eval(s3) ans = 8.9348 Example 4: S 3 x 1 1 x 3

2 2 s4=symsum((1/x)*(-1)^(x+1),1,inf) s4 = log(2) 1 x 1 S 4 1 x 1 x eval(s4) ans = 0.6931 4 Calculus: Taylor Series Math Review with Matlab U of M-Dearborn ECE Department Finite Summation Example

Example 5: N 1 2 S 5 x 1 x 3 N 2 N 15 N 31 6 x 1 syms x N; s5=symsum((x+3)*(x+1),1,N) s5 = 7/6*N-11/6+3/2*(N+1)^2+1/3*(N+1)^3 s5=simple(s5) s5 = 1/6*N*(31+15*N+2*N^2) 5 Calculus: Taylor Series Math Review with Matlab

U of M-Dearborn ECE Department Taylor Series Taylor Series approximation is defined as: f t ( x ) x a n n 0 f n (a) n! MacLaurin Series is the Taylor series approximation with a=0:

ft x n 0 n f n ( 0) n! 6 Calculus: Taylor Series Math Review with Matlab U of M-Dearborn ECE Department Taylor Command taylor(f) is the fifth order MacLaurin polynomial

approximation to f taylor(f,n) is the (n -1)-st order MacLaurin polynomial taylor(f,n,a) is the Taylor polynomial approximation about point a with order (n -1). 7 Calculus: Taylor Series Math Review with Matlab U of M-Dearborn ECE Department Taylor Series Example Given the function: f x ln 1 x 1) Find the first 6 Taylor Series Terms (a=0) 2) Find the first 4 terms about the point a=2 sym x; f=log(1+x) % Matlab's Natural Log f = log(1+x)

8 Calculus: Taylor Series Math Review with Matlab U of M-Dearborn ECE Department Taylor Series Terms Find the first 6 Taylor Series Terms (a=0) taylor(f) %Default is 5th order ans = x-1/2*x^2+1/3*x^3-1/4*x^4+1/5*x^5 Find the first 4 terms about the point a=2 Note that this is 3rd order taylor(f,4,2) ans = log(3)+1/3*x-2/3-1/18*(x-2)^2+1/81*(x-2)^3 9 Calculus: Taylor Series

Math Review with Matlab U of M-Dearborn ECE Department Taylor Series Approximation and Comparison Example Given the function: 1 f x 5 4 cos x 1) Plot f(x) from -2 to 2 2) Find the first 8 Taylor Series Terms (a=0) 3) Plot the approximation and compare against the original function f(x) 10 Calculus: Taylor Series Math Review with Matlab U of M-Dearborn ECE Department Plot f(x)

The easiest way to generate a graph is to use ezplot ezplot leaves the axes unlabeled syms x f=1/(5+4*cos(x)); ezplot(f,-2*pi,2*pi); grid on xlabel('x');ylabel('f(x)') 11 Calculus: Taylor Series Math Review with Matlab U of M-Dearborn ECE Department Plot of f(x) 12

Calculus: Taylor Series Math Review with Matlab U of M-Dearborn ECE Department Taylor Approximation To find the first 8 terms of the Taylor series approximation: ft_8=taylor(f,8) ft_8 = 1/9+2/81*x^2+5/1458*x^4+49/131220*x^6 1 2 x 2 5x 4 49 x 6 ft 9 81 1458 131220 13 Calculus: Taylor Series Math Review with Matlab U of M-Dearborn ECE Department

Comparison Plot approximation: hold on ezplot(ft_8) axis([-2*pi 2*pi 0 5]) Approximation is only good for small x Taylor approximation Original f(x) 14 Calculus: Taylor Series Math Review with Matlab U of M-Dearborn ECE Department Summary

The symbolic toolbox can be used to analyze definite and indefinite series summations Taylor series can be used to approximate functions MacLaurin series is a special case of the Taylor series approximated around x=0 Increase the number of terms to increase approximation accuracy 15