Ch2 - MATLAB Expressions Matlab has an interactive mode...

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Unformatted text preview: MATLAB Expressions Matlab has an interactive mode Many expressions are obvious (like addition, multiplication, etc.) Some expressions (exponentials, natural logarithms, Bessel Functions, etc.) are not as obvious The help , lookfor commands can be useful Variables can be stored in Matlab a = 5 b = 2^3+6 c = a+b Some variables are built in. Be careful, you can change them ans pi Inf NaN Matrices and Vectors Arrays are a collection of values referred to by a single variable name Matrices can be defined several different ways 1. Manual Entry 1. Expressions that evaluate a matrix 1. Built-in functions that return matrices 1. User-written functions that return matrices 1. Importing matrix data from files on disk Roger, Roger. Whats our vector, Victor? Airplane Vectors Matrices Manual Entry >> A = [4 6 7; 5 3 2; 1 7 4] A = 4 6 7 5 3 2 1 7 4 >> u=[6 3 8] u = 6 3 8 >> v = [3.1; 4.2; 0.5; 9.0] v = 3.1000 4.2000 0.5000 9.0000 The human mind has never invented a labor-saving machine equal to algebra. Anonymous Expressions (e.g. Transpose) >> A = [4 6 7; 5 3 2; 1 7 4]; >> B=A' B = 4 5 1 6 3 7 7 2 4 Built in functions diag, eye, ones, rand, length, linspace, logspace, zeros, size >> eye(4) % 4x4 Identity Matrix ans = 1 0 0 0 1 0 0 0 1 0 0 0 1 >> rand(3,4) % Matrix of random numbers between 0 and 1 ans = 0.8147 0.9134 0.2785 0.9649 0.9058 0.6324 0.5469 0.1576 0.1270 0.0975 0.9575 0.9706 More Built in Functions >> linspace(0,100,11) points ans = 0 10 20 30 40 50 60 70 80 90 100 >> x = logspace(1,5,3) x = 10 1000 100000 >> A = [1 3 5; 2 1 7; 4 3 2; 1 6 9]; 4 rows and 3 columns >> size(A) ans = 4 3 Subscript Notation >> A = [1 3 5; 2 1 7; 4 3 2; 1 6 9]; % A is 4x3 matrix >> A(2,3) % What is the value of A in the second row, 3 column? >> A(2,3)=6 % Change the value of A in the 2nd row and 3 column Colon Notation >> v = 1:10 % Create a vector starting at 1 and ending at 10 v = 1 2 3 4 5 6 7 8 9 10 >> u=1:2:10 % Create a vector starting at 1 going by twos u = 1 3 5 7 9 >> A = [1 3 5; 2 1 7; 4 3 2; 1 6 9]; % Create a 4x3 matrix >> A(:,2) % create a vector of the second column of A ans = 3 1 3 6 Math Matrix Operations Addition and Subtraction (u+v, u-v), Matrices must be same size At the source of every error which is blamed on the computer you will find at least two human errors including the error of blaming it on the computer. Anonymous Review matrix multiplication Dot Product >> A=ones(2,3); B=[1 2; 3 4; 5 6]; % Create Matrices >> A*B % Matrix Multiply ans = 9 12 9 12 >> u = [10 9 8 6]; v = [1;2;3;4]; % Create vectors >> u*v % Dot product really just matrix multiplication ans = 76 Vectorization and Array Operators In Matlab, function is applied to all elements >> x = 0:pi/4:pi x = 0 0.7854 1.5708 2.3562 3.1416 >> y = cos(x) y = 1.0000 0.7071 0.0000 -0.7071 -1.0000 Vectorization and Array Operators >> A = [1 2 3; 4 5 6; 7 8 9]; >> B = [9 8 7; 6 5 4; 3 2 1]; >> A.*B >> A....
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This note was uploaded on 09/14/2009 for the course MAN 320 taught by Professor Passovoy during the Spring '08 term at University of Texas at Austin.

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Ch2 - MATLAB Expressions Matlab has an interactive mode...

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