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MATLAB Programming

MATLAB Programming. fprintf Cell arrays Structures Flow of control Vectorization Functions. MATLAB Documentation for fprintf. fprintf Write data to text file Syntax fprintf (fileID,formatSpec,A1,...,An). My comments: fileID not used when printing to Command Window

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MATLAB Programming

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  1. MATLAB Programming fprintf Cell arrays Structures Flow of control Vectorization Functions

  2. MATLAB Documentation for fprintf fprintf Write data to text file Syntax fprintf(fileID,formatSpec,A1,...,An) My comments: fileID not used when printing to Command Window formatSpec enclosed in single quote marks: ‘string’ A1,…,Anare variables (or numbers) to be printed

  3. % print pi to 7 decimal places fprintf('%9.7f\n',pi) % f fixed-point number % a.b field width = a characters % b digits to the right of decimal point % \n newline 3.1415927

  4. % print a column of numbers x = [1.34, -2.45, 0.91]; fprintf('%5.2f\n',x) % There can be 2 characters on left. 1.34 -2.45 0.91

  5. Exercise Print as a fixed-point number to 12 decimal places.

  6. % print signed integers with field width 4 x = [198, -230, 3]; fprintf('%4d\n',x) 198 -230 3

  7. Exercise Create a vector containing the (integer) elements: 0,-1,2,-3. Print these numbers in a column with right justification.

  8. Cell Arrays A cell array can combine different data having different data types all in one array. A cell within a cell array is referenced by an index. A cell array is frequently an input argument of a function. This permits a collection of data (even of different data types) to be input to the function using a single argument.

  9. % create a cell array using braces {} y = {'scores',[73,38,81,55]}; y{3} = 'success'; celldisp(y) y{1} = scores y{2} = 73 38 81 55 y{3} = success

  10. % What is in the second cell of the cell array y? disp(y(2)) [1x4 double]

  11. % What values are in the second cell of the cell array y? disp(y{2}) 73 38 81 55

  12. % print values in the cell array y fprintf('%s: ',y{1}) fprintf('%2d ',y{2}) fprintf('\n') scores: 73 38 81 55

  13. % create a cell array using the function cell() x = cell(1,2); x{1} = 'salary'; x{2} = 45000; celldisp(x) x{1} = salary x{2} = 45000

  14. Exercise

  15. Structures A structure can combine different data having different data types under one banner. Each component of a structure is called a field. A structure array is an array, each element of which is a structure, and all structures in the structure array have the same set of fields.

  16. % simple structure a.label = 'x'; a.vect = 0:5; disp(a) label: 'x' vect: [0 1 2 3 4 5]

  17. Exercise

  18. % create structure array using function struct() c = struct('label',{'x','y'},'vect',{0:5,0:10}); disp(c) disp(c(1)) disp(c(2)) 1x2 struct array with fields: label vect label: 'x' vect: [0 1 2 3 4 5] label: 'y' vect: [0 1 2 3 4 5 6 7 8 9 10]

  19. % create 1 x 2 structure array c = struct('class',{71,72},'language',{'C','MATLAB'}); for n = 1:2 fprintf('ECE %2d: %s\n',c(n).class,c(n).language) end ECE 71: C ECE 72: MATLAB

  20. % structure array b(1).label = 'x'; b(2).label = 'y'; b(1).vect = 0:5; b(2).vect = 0:10; disp(b) disp(b(1)) disp(b(2)) 1x2 struct array with fields: label vect label: 'x' vect: [0 1 2 3 4 5] label: 'y' vect: [0 1 2 3 4 5 6 7 8 9 10]

  21. Exercise

  22. Flow of Control Redirection if else elseif Loops for

  23. Relational Operators

  24. Logical Operators

  25. % if for k = 0:3 if k == 2 disp(k) end end 2

  26. % if and else for k = 0:3 if k >= 2 disp(k) else disp([num2str(k),' < 2']) end end 0 < 2 1 < 2 2 3

  27. % elseif for k = 0:3 if k < 2 disp([num2str(k),' < 2']) elseif k == 2 disp(k) else disp([num2str(k),' > 2']) end end 0 < 2 1 < 2 2 3 > 2

  28. % or for k = 0:4 if k < 2 || k > 3 disp(k) end end 0 1 4

  29. % and (input number is 3) x = input('number: '); if x >= 1 && x <= 5 disp('between 1 and 5') end between 1 and 5

  30. Exercise Create a script that does the following:

  31. % Compare 2 methods of printing a vector tic for k = 0:9 % within this loop, k is a scalar fprintf('%1d ',k) end fprintf('\n') toc tic m = 0:9; fprintf('%1d ',m) % This is preferred. It is faster. fprintf('\n') toc 0 1 2 3 4 5 6 7 8 9 Elapsed time is 0.000264 seconds. 0 1 2 3 4 5 6 7 8 9 Elapsed time is 0.000077 seconds.

  32. % Add all even integers 0 through 100 x = 0; for m = 2:2:100 % even integers, 2 through 100 x = x + m; end fprintf('%4d\n',x) 2550

  33. Exercise Calculate the sum of all odd integers from 1 through 101.

  34. Vectorization Preallocation of memory Vectorizing Loops

  35. % Preallocation of memory N = 1000000; tic % frequent lengthening of x x(1) = 1; x(2) = 2; for n = 3:N x(n) = x(n-1)*x(n-2); end toc tic % FASTER: preallocation of memory for x y = ones(1,N); y(2) = 2; for n = 3:N y(n) = y(n-1)*y(n-2); end toc Elapsed time is 5.386562 seconds. Elapsed time is 2.242842 seconds.

  36. % Vectorizing a loop: linspace tic % slow phi = 0; dphi = 2*pi/100; g = zeros(1,1001); for n = 1:1001 g(n) = sin(phi); phi = phi + dphi; end toc tic % fast phi = linspace(0,20*pi,1001); h = sin(phi); toc Elapsed time is 0.002522 seconds. Elapsed time is 0.000136 seconds.

  37. Exercise Here is one way to generate samples of a sinewave: for n = 1:8 x(n) = sin(pi*(n-1)/4); end Enter the above code and display the results. Then vectorize this code and verify that your vectorized code gives the same results.

  38. Functions Function m-file Local variables Functions with multiple inputs/outputs

  39. function v = sphereVol(r) % calculates the volume of a sphere % input r = radius % output v = volume c = 4/3; v = c*pi*(r^3); end % sphereVol

  40. Local Variables Variables appearing in a function are local. These local variables do not appear in the MATLAB workspace and are not visible outside of the function in which they occur. For example, a variable c in the MATLAB workspace will be unaffected by a (local) variable c that appears within a function. Within the function, the local cis recognized and the workspace cis not. When the function returns, the local cis forgotten and the workspace cis again recognized. The input arguments of a function have local names. When the function returns, these local names are forgotten. The output variables of a function have local names. The values of these output variables are returned to the caller; however, the local names of these output variables are forgotten.

  41. % Script that calls the function sphereVol c = 2; radius = 1; vol = sphereVol(radius); fprintf('c = %3.1f, vol = %5.2f\n',c,vol) whos c = 2.0, vol = 4.19 Name Size Bytes Class Attributes c 1x1 8 double radius 1x1 8 double vol 1x1 8 double

  42. Exercise

  43. function [radius, angle] = rect2polar(x, y) % converts the (x,y) coordinates to polar coordinates % inputs: rectangular coordinates x and y % outputs: % radius = distance from origin % angle = angle (rad) measured counterclockwise from x axis radius = sqrt(x.^2 + y.^2); angle = atan2(y,x); end % rect2polar

  44. % Rectangular to polar coordinate conversions x = linspace(1,0,5); y = linspace(0,1,5); [r,theta] = rect2polar(x,y); table = [x; y; r; theta]; fprintf(' x y r theta\n') fprintf('%5.2f %5.2f %5.3f %5.3f\n',table) x y r theta 1.00 0.00 1.000 0.000 0.75 0.25 0.791 0.322 0.50 0.50 0.707 0.785 0.25 0.75 0.791 1.249 0.00 1.00 1.000 1.571

  45. Exercise

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