Question

Assume that A and B are MATLAB arrays with 10 rows and an equal number of columns (the number of columns is not given). Important: Next, the expression "a single line of code" implies a single command or equality. In other words, the code:

X=A+1; X=X+B; is considered to be TWO lines of code, even though it can be written as one line.

(a) (3%) Write a single line of code which saves the first two rows of array A as a new array X.

(b) (4%) Write a single line of code which replaces rows 4 and 5 of array A with rows 2 and 6 of array B.

(c) (3%) Write a single line of code which divides all elements in array A by the corresponding elements in array B and saves the resulted array as X.

(d) (4%) Write a single line of code which adds the transpose of array A to array B and saves the result in array X. What should the number of columns of A and B be so that this operation does not result in an error?

(e) (4%) Write a single line of code which uses the MATLAB function "sum()" to find the sum of each row

(f) (3%) Lets call N the unknown number of columns of arrays A and B. What is the size of array X = [A B]; ?

(g) (3%) Again, N is the number of columns of arrays A and B. What is the size of array X = [A;B]; ?

(h) (3%) Assume that the arrays A and B have more than 5 columns. Write a single line of code that divides all elements in A by the B element located at row 3 and column 4.

(i) (5%) Write a single line of code using the MATLAB function "find()" which finds the location of all elements in A which are greater than 1. Then, write another line of code which replaces all these elements in A by the number 2.

Answer 1

(i)

A = magic(10);
B = A';
X = A(1:2,:);

output:

>> A
A =

    92    99     1     8    15    67    74    51    58    40
    98    80     7    14    16    73    55    57    64    41
     4    81    88    20    22    54    56    63    70    47
    85    87    19    21     3    60    62    69    71    28
    86    93    25     2     9    61    68    75    52    34
    17    24    76    83    90    42    49    26    33    65
    23     5    82    89    91    48    30    32    39    66
    79     6    13    95    97    29    31    38    45    72
    10    12    94    96    78    35    37    44    46    53
    11    18   100    77    84    36    43    50    27    59

>> B
B =

    92    98     4    85    86    17    23    79    10    11
    99    80    81    87    93    24     5     6    12    18
     1     7    88    19    25    76    82    13    94   100
     8    14    20    21     2    83    89    95    96    77
    15    16    22     3     9    90    91    97    78    84
    67    73    54    60    61    42    48    29    35    36
    74    55    56    62    68    49    30    31    37    43
    51    57    63    69    75    26    32    38    44    50
    58    64    70    71    52    33    39    45    46    27
    40    41    47    28    34    65    66    72    53    59

>> X
X =

   92   99    1    8   15   67   74   51   58   40
   98   80    7   14   16   73   55   57   64   41

(ii)

A([4 5],:) = B([2 6],:);

after modification A is

A =

    92    99     1     8    15    67    74    51    58    40
    98    80     7    14    16    73    55    57    64    41
     4    81    88    20    22    54    56    63    70    47
    99    80    81    87    93    24     5     6    12    18
    67    73    54    60    61    42    48    29    35    36
    17    24    76    83    90    42    49    26    33    65
    23     5    82    89    91    48    30    32    39    66
    79     6    13    95    97    29    31    38    45    72
    10    12    94    96    78    35    37    44    46    53
    11    18   100    77    84    36    43    50    27    59

(iii)

X = A./B;

resultant X is

    1.000000    1.010204    0.250000    0.094118    0.174419    3.941176
    0.989899    1.000000    0.086420    0.160920    0.172043    3.041667
    4.000000   11.571429    1.000000    1.052632    0.880000    0.710526
   10.625000    6.214286    0.950000    1.000000    1.500000    0.722892
    5.733333    5.812500    1.136364    0.666667    1.000000    0.677778
    0.253731    0.328767    1.407407    1.383333    1.475410    1.000000
    0.310811    0.090909    1.464286    1.435484    1.338235    0.979592
    1.549020    0.105263    0.206349    1.376812    1.293333    1.115385
    0.172414    0.187500    1.342857    1.352113    1.500000    1.060606
    0.275000    0.439024    2.127660    2.750000    2.470588    0.553846

 Columns 7 through 10:

    3.217391    0.645570    5.800000    3.636364
   11.000000    9.500000    5.333333    2.277778
    0.682927    4.846154    0.744681    0.470000
    0.696629    0.726316    0.739583    0.363636
    0.747253    0.773196    0.666667    0.404762
    1.020833    0.896552    0.942857    1.805556
    1.000000    1.032258    1.054054    1.534884
    0.968750    1.000000    1.022727    1.440000
    0.948718    0.977778    1.000000    1.962963
    0.651515    0.694444    0.509434    1.000000

(iv)

X = A'+B; %A' denotes transpose

X =

   184   196     8   170   172    34    46   158    20    22
   198   160   162   174   186    48    10    12    24    36
     2    14   176    38    50   152   164    26   188   200
    16    28    40    42     4   166   178   190   192   154
    30    32    44     6    18   180   182   194   156   168
   134   146   108   120   122    84    96    58    70    72
   148   110   112   124   136    98    60    62    74    86
   102   114   126   138   150    52    64    76    88   100
   116   128   140   142   104    66    78    90    92    54
    80    82    94    56    68   130   132   144   106   118

number of columns should be 10 as it is to be square