Compound matrix: Difference between revisions

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m Relation to adjugate matrices: The usual adjugate is the 1st order adjugate, if we maintain the convention that I,J are r-sets
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{{see also|Adjugate matrix}}
 
Let {{math|''A''}} be an {{math|''n'' × ''n''}} matrix. Recall that its '''{{math|''r''}}th higher adjugate matrix''' {{math|adj<sub>''r''</sub>(''A'')}} is the <math display="inline">\binom{mn}{r} \times \binom{n}{r}</math> matrix whose {{math|(''I'', ''J'')}} entry is
:<math>(-1)^{\sigma(I) + \sigma(J)} \det A_{J^c, I^c},</math>
where, for any set {{math|''K''}} of integers, {{math|''σ''(''K'')}} is the sum of the elements of {{math|''K''}}. The '''adjugate''' of {{math|''A''}} is its {{math|(''n'' &minus; 1)}}st1st higher adjugate and is denoted {{math|adj(''A'')}}. The generalized [[Laplace expansion]] formula implies
:<math>C_r(A)\operatorname{adj}_r(A) = \operatorname{adj}_r(A)C_r(A) = (\det A)I_{\binom{n}{r}}.</math>