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A4-format til udskrift. - Aarhus Universitet

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1. VEKTORER OG MATRICER 167<br />

1.16. 3x4 matrix<br />

Eksempler<br />

☞ [LA] 2 Matricer<br />

3 × 4-matrix ⎛<br />

1 2 0<br />

⎞<br />

−2<br />

⎝−1<br />

8 3 4 ⎠<br />

5 4 3 1<br />

4-rækkematrix<br />

<br />

6 2 9<br />

<br />

−2<br />

3-søjlematrix<br />

⎛ ⎞<br />

5<br />

⎝ 0 ⎠<br />

−5<br />

1.17. Addition skalering ☞ [LA] 2 Matricer<br />

Definition<br />

Sum, Skalarmultiplikation<br />

To m × n-matricer kan adderes <strong>til</strong> en m × n-matrix. En matrix kan skaleres.<br />

Eksempel<br />

<br />

1 2<br />

+<br />

−1 8<br />

A = (aij)i=1...m,j=1...n<br />

B = (bij)i=1...m,j=1...n<br />

A + B = (aij + bij)i=1...m,j=1...n<br />

λA = (λaij)i=1...m,j=1...n<br />

<br />

1 2<br />

=<br />

−1 8<br />

<br />

2 4<br />

= 2<br />

−2 16<br />

<br />

1<br />

<br />

2<br />

−1 8<br />

1.18. Matrix multiplikation ☞ [LA] 2 Matricer<br />

Definition (Multiplikation)<br />

En m × n-matrix og en n × p-matrix kan multipliceres (ganges sammen) <strong>til</strong> en m × pmatrix.<br />

A = (aij)i=1...m,j=1...n<br />

B = (bjk)j=1...n,k=1...p<br />

AB = (cik)i=1...m,k=1...p<br />

cik = ai1b1k + · · · + ainbnk =<br />

n<br />

j=1<br />

aijbjk<br />

1.19. Gange er nemt ☞ [LA] 2 Matricer<br />

Bemærkning<br />

I cik indgår kun den i-te række i første matrix og den k-te søjle i anden matrix.<br />

⎛ ⎞<br />

cik = ⎜<br />

⎜<br />

ai1 ...aij ...ain ⎜<br />

⎝<br />

b1k<br />

.<br />

bjk<br />

.<br />

bnk<br />

⎟<br />

⎠<br />

= ai1b1k + · · · + aijbjk + · · · + ainbnk

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