MATLAB Primer
MATLAB as a calculator • Built in functions Toolbox: statistics, image processing, signal processing, Wavelet, control… >> help >> help stats rand(), randperm(); • Built in Variables pi, sin(pi/6) 

The Real Power of MATLAB • e.g. solving linear equations in one step


Programming Environment • Three windows: command window, workspace and command history • Three ways to get help: >> help sqrt >> lookfor sqrt >> doc sqrt 

All MATLAB variables are matrices • “MATrix LABoratory” • A vector is a matrix with one row or one column • a scalar is a matrix with one row and one column • a character string is a row of column vector of characters 

Assigning Values to Variables
• >> A = [ 3, 2; 3 1; 1 5] 

Using functions to create matrices and vectors • linspace >> u = linspace(0,5,5) How to create column vectors? • Create matrices ones, zeros , eye, diag A closer look at diag(). 

Notation • Subscript notation • Colon notation >> s = 1 : 4 >> s = 1 :0.5: 4 • Use colon notation to refer to subsets of columns and rows >> A(1:2,1) >> A(:,1) 

String Operations • String are matrices with character elements. • String constants are enclosed in single quotes. 

String Functions • Compare two strings to see if they are exactly the same strcmp(‘abc’, ‘abd’); • Search for a substring with a longer string findstr(‘abcdef’, ‘def’); findstr(‘abcdefdfadfadfdef’,’def’); • help string strcat(‘chen’,’ yu’); 

Builtin Functions • Scalar function sin cos tan exp log sqrt floor ceil abs • Vector functions max min sum sort median mean They also work for matrices. • Matrix functions eig inv size rank 

Working space • who/whos/clear • save • Path 

Vectorization • Use vectorized indexing and logical functions • Use vector operations instead of loops e.g. C = A ./3; A^2 vs. A .^2 • Pre allocate memory for vectors and matrices 

Vectorized Indexing • x = [ 0.2, 0.55, 0.3,3, 0.7, 1]; index = find(x>0.5) x(index) • find(x==1) • x(find (abs(x1.5) > 0.5)) 

Why it is important? Problem: construct an 50000 entry array Method 1:


Comparing the times in these three methods 
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