Visualising 2D Arrays in Matlab - KURSUS MATLAB ONLINE Skripsi, Tesis, DISERTASI 081219449060

19.2       Visualising 2D Arrays in Matlab • One common view of 2D arrays is: -              a series of numbered boxes -              boxes are arranged into rows and columns and are numbered on that basis -              each box may hold a single data value -              each particular box is addressed by using its row and column number -              the collection of boxes together has the name of the array 19.3       Visualising 2D Arrays Example • For example a table of network traffic collected hourly over several days: -              the array (matrix) is called traffic -              it has 7 rows (corresponding to the days of the week), and 24 columns (corresponding to the hours of the day) -              hence it has 168 elements - element number (2,23) [row 2, column 23] contains the value 11.8 19.4       Creation • Creation of 2D arrays follows the same principles as for vectors: - square brackets - spaces or commas to separate values on a row -              semi-colon or <returns> to separate rows • For example: >>  square2 = [ 1 2 ; 3 4] square2 =      1     2      3     4 19.5       Creation Example >>  firstLine = 1:5 firstLine =      1     2     3     4     5 >> secondLine = 6:10 secondLine =      6     7     8     9    10 >> rect2 = [firstLine ; secondLine] rect2 =      1     2     3     4     5      6     7     8     9    10 >>  rect5 = rect2' rect5 =      1     6      2     7      3     8      4     9      5    10 >> diary off 19.6       Mathematics of Matrices • Mathematical operations with matrices follow the rules previously presented for vectors: -              operations with scalars are applied individually to elements of the matrix -              operations involving two matrices follow the mathematical definition for that operation on two matrices -              special “dot” operators have been provided to allow element by element operations for two matrices • For example: >> square2 square2 =      1     2      3     4 >> 2-square2 ans =      1     0     -1    -2 >> 10*square2 ans = 10    20 30    40 19.7       Mathematics Example >> long=[square2 square2*10 square2(:,1)*100] long =      1     2    10    20   100      3     4    30    40   300 >> rect2 rect2 =      1     2     3     4     5      6     7     8     9    10 >> sum = long+rect2 sum =      2     4    13    24   105      9    11    38    49   310 >> 2.^square2 ans =      2     4      8    16 Mathematics Example (Cont) >> rect5 rect5 =      1     6      2     7      3     8      4     9      5    10 >> rect2*rect5 ans =     55   130    130   330 >> rect5*rect2 ans =     37    44    51    58    65     44    53    62    71    80     51    62    73    84    95     58    71    84    97   110     65    80    95   110   125 >> long./rect2 ans =     1.0000    1.0000    3.3333    5.0000   20.0000     0.5000    0.5714    3.7500    4.4444   30.0000 >> long/rect2 ans =    29.2400   -7.6400    85.7200  -22.7200 Mathematics Example (Cont) >> format short g >> long.^rect2 ans =             1            4         1000      1.6e+05        1e+10           729        16384    6.561e+11   2.6214e+14   5.9049e+24 >> diary off 19.8       Addressing & Manipulation • Elements of a matrix are specified using: -              name of the matrix and circle brackets -              row and column number(s) (separated by comma) of elements to be addressed.

• For example: >> ex1 = [1 4 7; 2 5 8; 3 6 9] ex1 =      1     4     7      2     5     8      3     6     9 >> ex2 = ex1' ex2 =      1     2     3      4     5     6      7     8     9 >> ex2(2,3) ans =      6 >> ex1(2,3) ans =      8 19.9       Addressing & Manipulation Example >> ex1(2,2)=-5 ex1 =      1     4     7      2    -5     8      3     6     9 >> ex1(2,5) = -5 ex1 =      1     4     7     0     0      2    -5     8     0    -5      3     6     9     0     0 >> ex1(:,4)=[10 11 12] ???  In an assignment  A(:,matrix) = B, the number of elements in the subscript of A and the number of columns in B must be the same.