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Intro

Intro. MATLAB: Special Purpose Computer Program Optimized to perform engineering and scientific calculations Implements the MATLAB programming language Has an extensive library of predefined functions. Advantages and disadvantages. Advantages: Easy to use Interpreted, not compiled

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Intro

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  1. Intro • MATLAB: Special Purpose Computer Program Optimized to perform engineering and scientific calculations • Implements the MATLAB programming language • Has an extensive library of predefined functions

  2. Advantages and disadvantages • Advantages: • Easy to use • Interpreted, not compiled • Integrated editor/debugger • Platform Independence • Works on Windows, Linux, Unix, and MacIntosh • Many predefined functions • E.g., arithmetic mean, standard deviation, median, etc. • Disadvantages: • Interpreted, not compiled • May execute more slowly

  3. Command Window • In command window, can type: • area=pi*2.5^2 • If line is too long , can add … to end of line to continue it on the next line • E.g., • x1 = 1 + ½ + 1/3 + ¼ + 1/5 + 1/6 • x1 = 1 + ½ + 1/3 + ¼ …+ 1/5 + 1/6 • Note the space between ¼ and …!

  4. Edit/Debug Window • Can create new Matlab files or modify existing ones • Created automatically when you create a new M-file or open an existing one • Select File->New->Blank M-file from the desktop menu • Select File->Open from the desktop menu • In edit window, type:%This m-file calculates the area of a circle.%and displays the result.radius = 2.5;area = pi * 2.5^2;string = [‘The area of the circle is ‘ num2str(area)];disp(string); • Save file as calc_area.m • Run by typing calc_area in Command Window

  5. Figure Windows • Used to display MATLAB graphics • Can be a two- or three-dimensional plot of data, an image, or a GUI • Write program to plot sin x: • %sin_x.m: This M-file calculates and plots the %function sin(x) for 0 <= x <= 6.x = 0:0.1:6y = sin(x)plot (x,y) • Save as sin_x.m and type sin_x into Command Window

  6. Getting Help in MATLAB • Use the Help Browser • ? Icon in desktop toolbar • Type “helpdesk” or “helpwin” in Command Window • Type “help” or “help” followed by function name in Command Window • “help” -displays a list of possible help topics • “help” function – displays help for that function • “lookfor” command • Searches summaries of each function for a match • Helpful in finding a function you don’t know the name of • E.g., suppose you wanted to find a function that takes the inverse of a matrix. • There’s no function called “inverse” • Do “lookfor inverse” • Get: • INVHILB Inverse Hilbert Matrix • ACOS Inverse cosine • ACOSH Inverse Hyperbolic cosine • ACOT Inverse Cotangent • ACSC Inverse cosecant • ACSCH Inverse Hyperbolic secant • ASIN Inverse sine • ASINH Inverse Hyperbolic sine • ATAN Inverse Tangent • Etc.

  7. Other Useful Commands • “demo” in command window (or select demos from the start button • Gives you demos of MATLAB’s capabilities • “clc” in command window • Clears content of command window • “clf” in command window • Clears content of figure window • “clear” in command window • Clears content of workspace • Good idea to avoid variables in one program affecting results in another program • Abort command (Ctrl-C) • Stops a running program • Good for infinite loops • “!” – sends commands to operating system and they are executed as if they’re typed into the operating system’s command prompt • Lets you embed op sys commands into MATLAB programs • “diary” filename • Once typed, all input and most output will be echoed into the diary file. • Helps find problems • To stop: type “diary off” • To continue: type “diary on”

  8. Matlabvs Python • Python Functions: def func(x): “”” Summary of this function goes here Detailed explanation goes here “”” return(x*x) • Matlab function [y] = func( x ) %Summary of this function goes here %Detailed explanation goes here y = x*x end

  9. Python vsMatlab def func(): inp= input('would you like to continue?') totalcost = 0 while (inp =='yes'): totalcost = totalcost + 3 inp = input('Would you like to buy something else?') return totalcost Matlab: function [totalcost ]= func() inp = input('would you like to continue?','s'); totalcost = 0; while (strcmpi(inp,'yes') == True) totalcost = totalcost + 3; inp = input('Would you like to buy something else?','s'); end end

  10. Python Vs Matlab arr = [3, 2, 8, 1, 4, 7, 9] k = len(arr) print(k) total = 0 for i in range (0,k): total = total + arr[i] print(total); Matlab: arr = [3 2 8 1 4 7 9] k = length(arr); disp(k) total = 0; for i=1:k %Note where loop starts!!! total = total + arr(i); end disp(total)

  11. Matlabvs Python arr = [3, 2, 8, 1, 4, 7, 9] k = length(arr) print(k) total = 0 for i in range (0,k,2): total = total + arr[i] print(total); Matlab: arr = [3 2 8 1 4 7 9] k = length(arr); disp(k) total = 0 for i=1:2:k %Note where increment is!!! total = total + arr(i); end disp(total);

  12. Vectors In Matlab • A vector is a list of numbers expressed as a 1 dimensional array. • A vector can be n×1 or 1×n. • Columns are separated by commas (or spaces): h= [1, 2, 3] • Rows are separated by semicolons: v = [1; 2; 3]

  13. Matrices in Matlab Columns • A matrix is a two dimensional array of numbers. • For example, this is a 4×3 matrix: • m=[3.0, 1.8, 3.6; 4.6, -2.0, 21.3; 0.0, -6.1, 12.8; 2.3, 0.3, -6.1] Rows

  14. Defining (or assigning) arrays • 12 18 -3 • 2 5 2 • 1 1 2 • 0 -2 6 • An array can be defined by typing in a list of numbers enclosed in square brackets: • Commas or spaces separate numbers. • A = [12, 18, -3] or A = [12 18 -3] • Semicolons indicate a new row. • B = [2, 5, 2; 1, 1, 2; 0, -2, 6]

  15. Array vs. Matrix Operations • Example: x = [2,1; 3,4] y = [5,6; 7,8] 2 1 5 6 3 4 7 8 z = x .* y results in [ 10, 6 21, 32] this is array multiplication z = x * y results in [ 17, 20; 43, 50] this is matrix multiplication So, do NOT forget the dot if you want to do array operations! (.* ./ .^)

  16. Matrix vs Array Multiplication a = [ 10 5 2 9 ] b = [ 1 3 2 4 ] c = [ 2 3 ] d = [ 2 3 ] • Multiply a .* b 10 15 4 36 • a * b 20 50 20 42 • b * c 11 16 • b .* c error • b * d • error • b .* d • error

  17. Left division: b = [ 2 3 ] a = [ 10 5 2 9 ] • q = b\a is equivalent to a x q = b 10x + 5y = 2 2x + 9y = 3 x = .2 - .5y x = 1.5 -4.5y .2 - .5y = 1.5 – 4.5y 4y=1.3 y = .325 x = .2 - .5x.325 x = .0375 • So q = [ 0.0375 ; 0.3250 ] • (right division: q=a/b is q x a = b, but rarely used!)

  18. Example:We know the following: • In combining colors: • If you combines 7 drops of a red hue, 12 drops of green hue, and 8 drops of the blue hue, you get a saturation of 143 • If you combines 3 drops of red, 6 drops of green and 14 drops of blue you get a saturation of 84 • If you combines 12 drops of red, 2 drops of green, and 4 drops of blue, you get a saturation of 152. • First, write this as a system of 3 linear equations: 7x + 12y + 8z = 143 3x + 6y + 14z = 84 12x + 2y + 4z = 152 • Next, in matlab, write the matrices representing these equations.  A= [7 12 8; b=[143; 3 6 14; 84; 12 2 4] 152] • Now, in matlab, write the equation that would solve for the 3 variables (red-saturation, green-saturation, and blue-saturation) Sol = b\a Sol: [ .0608, .0499, .0579]

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