Typing G(:) outputs the content of G in one column format.
d)
What do you get if you type G(7) and hit return? Can you explain how MATLAB got that answer? Try G(16) to confirm your answer.
ans =
6
Typing G (7) outputs the 7
th
element of G in the column or in row/column format it
’
s G(1,2)
G(16)
ans =
3
Typing G (16) outputs the 16
th
element of G in the column or in row/column format it
’s
G(4,3)
e)
What happens if you type G(12,1) and hit return?
ANSWERS:
G(12,1)
Index exceeds matrix dimensions.
Typing G (12,1) Matlab outputs
“
Index exceeds matrix dimensions.
”
G on has 6 rows, the 12
gave the error.
f)
What happens if you type G(G>5) and hit return? Can you explain how
MATLAB got that answer? What happens if you type G(G>5) = 100 and
hit return? Can you explain how MATLAB got that answer?
ANSWERS:
G(G>5)
ans =
6
9
Typing G (G>5) Matlab outputs the elements of G that are greater than 5.
G(G>5) = 100
G =
2
100
0
0
1
0
3
100
0
0
0
1
0
0
1
2
0
0
0
0
3
4
0
0
1
0
0
0
4
5

0
1
0
0
5
3
Typing G (G>5) = 100, Matlab find elements that are greater than 5 and replace that 5 then
outputs G with the replaced G>5 with 100.
6.
See the structure of a matrix: Create a 20 × 20 matrix with the command
A = ones(20); Now replace the 10 × 10 submatrix between rows 6:15 and
columns 6:15 with zeros. See the structure of the matrix (in terms of
nonzero entries) with the command spy(A). Set the 5 × 5 submatrices in
the top right corner and bottom left corner to zeros and see the
structure again. NOTE: Use semicolon to suppress the output for all the
matrices in this problem. In your lab-write up include the pictures
obtained with the spy command. To include the pictures, open your diary
file using a word processor such as MS Word then, on the MATLAB figure,
select “Edit” and “Copy Figure”, and paste the picture into the Word
file. Make sure you crop and resize the picture so that it does not
take up too much space.
ANSWERS:
A = ones(20), creates 20x20 matrix with elements of ones
B = zeros(20), creates 20x20 matrix with elements of zeros
A(6:15,6:15) = B(6:15,6:15), creates 10x10 submatrix and inserted to A: See Figure 1.
FIGURE 1:
A(16:20,16:20) = B(16:20,16:20) and A(1:5,1:5) = B(1:5,1:5), creates 5x5 submatrix top-
right and bottom-left with zeros elements. See figure 2.

FIGURE 2:
7.
Create a symmetric matrix: Create an upper triangular matrix with the
following command:

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