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Linear Algebra, Theory And Applications, 2012a

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108 ROW OPERATIONS<br />

Denote by E (c, i) this elementary matrix which multiplies the i th row of the identity by the<br />

nonzero constant, c. Then from what was just discussed and the way matrices are multiplied,<br />

⎛<br />

⎞<br />

a 11 a 12 ··· ··· a 1p<br />

. .<br />

.<br />

E (c, i)<br />

a i1 a i2 ··· ··· a ip<br />

⎜<br />

⎟<br />

⎝ . .<br />

. ⎠<br />

a n1 a n2 ··· ··· a np<br />

equals a matrix having the columns indicated below.<br />

⎛ ⎛ ⎞ ⎛ ⎞<br />

⎛<br />

a 11<br />

a 12<br />

. . =<br />

E (c, i)<br />

a i1<br />

,E(c, i)<br />

a i2<br />

, ··· ,E(c, i)<br />

⎜ ⎜ ⎟ ⎜ ⎟<br />

⎜<br />

⎝ ⎝<br />

. ⎠ ⎝<br />

. ⎠<br />

⎝<br />

a n1<br />

a n2<br />

⎛<br />

⎞<br />

a 11 a 12 ··· ··· a 1p<br />

.<br />

.<br />

.<br />

=<br />

ca i1 ca i2 ··· ··· ca ip<br />

⎜<br />

⎟<br />

⎝<br />

.<br />

.<br />

. ⎠<br />

a n1 a n2 ··· ··· a np<br />

This proves the following lemma.<br />

a 1p<br />

. .<br />

a ip<br />

.<br />

a np<br />

⎞⎞<br />

⎟⎟<br />

⎠⎠<br />

Lemma 4.1.4 Let E (c, i) denote the elementary matrix corresponding to the row operation<br />

in which the i th row is multiplied by the nonzero constant, c. Thus E (c, i) involves<br />

multiplying the i th row of the identity matrix by c. Then<br />

E (c, i) A = B<br />

where B is obtained from A by multiplying the i th row of A by c.<br />

Finally consider the third of these row operations. Denote by E (c × i + j) the elementary<br />

matrix which replaces the j th rowwithitselfaddedtoc times the i th row added to it. In<br />

case i

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