Xiang Li. Temple University. September 27, 2016

Transcription

1 Introduction to Matlab Xiang Li Temple University September 27, 2016

2 Outline u u u u Loops Functions Data Import Data export

3 While and For loops u u u Matlab has loops, similar to what you have seen in Java or C Matlab doesn't use braces ({,}) to enclose blocks so loops(and functions) need to be explicitly ed with the "" command For loop example for x 1:10 x

4 while loop u x = 1 while x <= 10 x x = x + 1;

5 while loop u Example: a = 10; while(a < 20) fprintf('value of a: %d\n', a) a = a + 1;

6 for loop u Example: for a = 1:10 fprintf('value of a: %d\n', a)

7 for loop u Example: for a = 10 : -1 : 1 fprintf('value of a: %d\n', a)

8 for loop u Example: for a = [24,18,17,23,28] fprintf('value of a: %d\n', a)

9 nested loop u Example: for a = 1 : 3 for b = ['a','b','c','d','e','f','g'] fprintf('%d %c', a, b) fprintf('\n');

10 nested loop u Given A = [ ; ; ; ] How many ones in A?

11 nested loop u Given A = [ ; ; ; ] How many ones in A? [row col] = size(a) numofone = 0; for i = 1:row for j = 1:col if A(i, j) == 1 numofone = numofone + 1; numofone

12 nested loop u Exercise: Write a program that outputs: 1a 1b 1c 1d 1e 1f 1g 2a 2b 2c 2d 2e 2f 2g 3a 3b 3c 3d 3e 3f 3g Use both 'while loop' and 'for loop'

13 Solution u Example: a = 1; while a <= 3 for b = ['a','b','c','d','e','f','g'] fprintf('%d %c', a, b) a = a + 1; fprintf('\n')

14 Function A function is a group of statemnets that together perform a task. In Matlab, functions are defined in separate files. The name of the file and of the function should be the same.

15 Function function max = mymax(n1, n2, n3) max = n1 if n2 > max max = n2 if n3 > max max = n3

16 Function function max = mymax(n1, n2) %This function calculates the maximum of the %five numbers given as input max = n1 if n2 > max max = n2

17 Sub-Function Primary functions can be called from outside of the file that defines them, either from command line or from other functions, but sub-functions cannot be called from command line or other functions, outside the function file.

18 Sub-Function function result = mypower(a) result = myrand(100); function randnum = myrand(b) randnum = round(rand * b);

19 Import data from the file Let's start with importing an image filename = 'haha.jpg'; A = importdata(filename); image(a)

20 Import data from the file filename = 'myfile.txt'; delimiterin = ' '; headerlinesin = 1; A = importdata(filename,delimiterin,headerlinesin);

21 Import data from the file filename = 'myfile.txt'; delimiterin = ' '; headerlinesin = 2; A = importdata(filename,delimiterin,headerlinesin);

22 Import data from the file Try: B = A.data C = A.textdata D = A.colheaders What are datatypes of B, C, D?

23 Cell u A cell array is a data type with indexed data containers called cells, where each cell can contain any type of data. u Cell arrays commonly contain either lists of text strings, combinations of text and numbers, or numeric arrays of different sizes. u Refer to sets of cells by enclosing indices in smooth parentheses, (). Access the contents of cells by indexing with curly braces, {}.

24 Cell C = A.textdata D = A.colheaders C and D are both 1*7 cell singletextdata1 = C{1, 3} singletextdata2 = D(1, 3)

25 load u matrix = load('data.txt')

26 Data export a = 10; fp = fopen('output.txt', 'a'); fprintf(fp, 'Value of a is %d', a); fclose(fp);

27 Precision a = ; fprintf(fp, 'Value of a is %0.2f\r\n', a); fprintf(fp, 'Value of a is %.3f\r\n', a); fprintf(fp, 'Value of a is %10.6f\r\n', a);

28 Precision fprintf(fid, '%.2f', x) specifies 2 decimal places but no particular width. fprintf(fid, '%5.2f', x) specifies two decimal places and a 5-character width.