ECE 8010
Homework #4 Solutions
1. (Exercise) The elementary row operations used to find reduced row echelon form of a matrix are (i)
scaling row i by , (ii) swapping row i and row j, and (iii) replacing row i with t
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ECE 8010
Homework #4 Solutions
1. (Exercise) The elementary row operations used to find reduced row echelon form of a matrix are (i)
scaling row i by , (ii) swapping row i and row j, and (iii) replacing row i with the sum of row i and
row j.
a. Performing an elementary row operation on a matrix A is equivalent to multiplying A on the
left by an appropriate square matrix M , i.e. MA. For each of the elementary row operations,
describe the form of the matrix M and check that the matrix is full rank.
b. Similarly, elementary column operations are equivalent to right multiplication by an
appropriate square matrix M , i.e. AM . For each of the elementary column operation,
describe the form of the matrix M and check that the matrix is full-rank.
2. (Exercise) Let : n n , : n m , : m m be linear transformations such that
( ) n and ( ) m . Use the Sylvester Inequality to show that ( ) ( ) .
3. Let : n n A , : m n B , : m m C be linear transformations. (The notation A B C , , will be
used for the transformation as well as the corresponding matrix representation of the transformation
when the standard bases are used for the domain and codomain.) Let A and C be full rank.
a. Show that ( ) ( ) AB B
b. Find a counterexample to demonstrate that in general ( ) ( ) BC B
c. Show that ( ) ( ) BC B
d. Find a counterexample to demonstrate that in general ( ) ( ) AB B
e. (Exercise) Can you find a condition related to m , n , and ( ) B that will guarantee that the
columns B form a basis for ( ) B ?
Note that 3a is a stronger statement than ( ) ( ) AB B . While ( ) ( ) AB B implies ( ) ( ) AB B , the
converse is not true. Similarly for 4b, ( ) ( ) BC B implies ( ) ( ) BC B , but the converse is not true.
4. (Exercise) True/False: (Provide a proof if true, or a counterexample if false.)
a. A full rank linear transformation is always onto.
b. A full rank linear transformation is always 1:1.
c. A square, full rank linear transformation is always 1:1
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