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Offline dg1727  
#1 Posted : 27 May 2010 13:10:21(UTC)
dg1727


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Man

Hello,

Could someone please point me to a definition of the alg() function?

In SMath Studio version 0.88, the description is "Algebraic addition to matrix."

In a Web search, the closest I found to a definition was a Wikipedia page on matrix addition, but I didn't find an operation which takes a matrix and 2 scalars as inputs and returns a scalar as output, as alg() does.

Thanks in advance for explaining.

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Offline Andrey Ivashov  
#2 Posted : 27 May 2010 15:55:57(UTC)
Andrey Ivashov


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It's a Cofactor.

Regards.
Offline oscampo  
#3 Posted : 27 May 2010 16:32:11(UTC)
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Hi,
The alg() returns the cofactor of a matrix, wich is defined as el(A;i;j)=(-1)^(i+j)*el(M;i;j), where el(M;i;j) is the minor of a matrix.

In the help for alg() function you can see:
alg(mat(1;2;3;4;5;6;7;8;9;3;3);1;2)=6

For matrix A←mat(1;2;3;4;5;6;7;8;9;3;3), The minor el(M;1;2) of A is:
el(M;1;2)←det(mat(#;#;#;4;#;6;7;#;9;3;3))
el(M;1;2)←det(mat(4;6;7;9;2;2))

so, el(A;1;2) is the cofactor of A, calculated as:
el(A;1;2)Sad-1)^(1+2)*(4*9-7*6)=6.

Regards,

Oscar Campo
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