1 / 55

Advanced MATLAB

Advanced MATLAB. Vectors and matrices fprintf Cell arrays Structures Flow of control Vectorization Functions. Using an Index to Address Elements of an Array. In the C/C++ programming language, an index starts at 0 and elements of an array are addressed with square brackets [∙] :

colin
Download Presentation

Advanced MATLAB

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Advanced MATLAB Vectors and matrices fprintf Cell arrays Structures Flow of control Vectorization Functions

  2. Using an Index to Address Elements of an Array In the C/C++ programming language, an index starts at 0 and elements of an array are addressed with square brackets [∙]: 8 2 -3 7 -1 x[0] x[1] x[2] x[3] x[4] ↑ ↑ ↑ ↑ ↑ In MATLAB, an index starts at 1 and elements of an array are addressed with parentheses (∙): 8 2 -3 7 -1 x(1) x(2) x(3) x(4) x(5) ↑ ↑ ↑ ↑ ↑

  3. Columns, Rows, and Pages for a 2-Dimensional Array (Matrix) x(m,n) m is the row number n is the column number x(m,n)is the element of the matrix x that is: in the mth row in the nthcolumn

  4. Columns, Rows, and Pages for a 3-Dimensional Array x(m,n,p) m is the row number n is the column number p is the page number x(m,n,p) is the element of the 3-dimensional array x that is: in the mth row in the nth column on the pth page

  5. % scalars, vectors, matrices, 3-dimensional arrays a1 = zeros(1,1); % scalar disp(['a1: ',num2str(size(a1))]) a2 = zeros(1,4); % vector disp(['a2: ',num2str(size(a2))]) disp(a2) a3 = zeros(2,2); % matrix disp(['a3: ',num2str(size(a3))]) disp(a3) a4 = zeros(2,2,3); % 3-dimensional array disp(['a4: ',num2str(size(a4))]) a1: 1 1 a2: 1 4 0 0 0 0 a3: 2 2 0 0 0 0 a4: 2 2 3

  6. Exercise

  7. % Editing arrays with parentheses () B = [1 2 3 4; 5 6 7 8]; disp('before:') disp(B) b = [0 0]'; B(:,4) = b; disp('after:') disp(B) before: 1 2 3 4 5 6 7 8 after: 1 2 3 0 5 6 7 0

  8. Exercises Create a matrix of zeros with 3 rows and 4 columns. Create a matrix with 2 rows and 2 columns, with all elements equal to 5. Insert the smaller matrix into the lower right-hand corner of the larger matrix. Hints: zeros()5*ones()

  9. % array versus matrix multiplication a = [1 2; 3 4]; disp(a*a) % matrix multiplication disp(a.*a) % array multiplication 7 10 15 22 1 4 9 16

  10. % array multiplication, division, and power x = [1 4; 9 8]; y = [1 2; 3 4]; disp(x.*y) % array multiplication: .* disp(x./y) % array division: ./ disp(x.^2) % array power: .^ 1 8 27 32 1 2 3 2 1 16 81 64

  11. Exercise

  12. 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

  13. % 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

  14. % 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

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

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

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

  18. 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.

  19. % 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

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

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

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

  23. % 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

  24. Exercise

  25. 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.

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

  27. Exercise

  28. % 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]

  29. % 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

  30. % 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]

  31. Exercise

  32. Flow of Control Redirection if else elseif Loops for

  33. Relational Operators

  34. Logical Operators

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

  36. % 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

  37. % 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

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

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

  40. Exercise Create a script that does the following:

  41. % 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.

  42. % 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

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

  44. Vectorization Preallocation of memory Vectorizing Loops

  45. % Preallocation of memory tic % SLOW: frequent lengthening of x x(1) = 1; x(2) = 1; for n = 3:100000 x(n) = x(n-1)*x(n-2); end toc tic % FAST: preallocation of memory for x y = ones(1,100000); for n = 3:10000 y(n) = y(n-1)*y(n-2); end toc Elapsed time is 0.526046 seconds. Elapsed time is 0.021451 seconds.

  46. % 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.

  47. 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.

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

  49. 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

  50. 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.

More Related