# Ch 2 - MATLAB Expressions Matlab has an interactive mode...

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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 –T h e 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 –p i –I n f –N a N 1 Matrices and Vectors Arrays are a collection of values referred to by a single variable name

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•V e c t o r s 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 3 Expressions (e.g. Transpose) >> A = [4 6 7; 5 3 2; 1 7 4]; >> B=A' B = 4 5 1 6 3
Built in functions diag, eye, ones, rand, length, linspace, logspace, zeros, size >> eye(4) % 4x4 Identity Matrix ans = 1 0 0 0 0 1 0 0 0 0 1 0 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 5 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 6

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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 rd column? ans = 7 >> A(2,3)=6 % Change the value of A in the 2nd row and 3 rd column A = 1 3 5 2 1 6 4 3 2 1 6 9 7 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 8
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 9 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 10

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## This note was uploaded on 01/29/2011 for the course PGE 310 taught by Professor Klaus during the Spring '06 term at University of Texas.

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Ch 2 - MATLAB Expressions Matlab has an interactive mode...

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