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4x4 Matrixby phantomAI
Tags: matrix 
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#1
Mar2204, 09:25 AM

P: 17

I seem to be still having problems with solving the determinant of a 4x4 matrix correctly. There are two methods I can use: Factor/Cofactor and reduction to triangular form.
Ex: [ 1 2 3 4 5 2 1 0 6 4 3 2 1 1 1 1] determinant is 2 based on the calculator Factor/Cofactor: I did: 1*det[2,1,0; 4,3,2; 1,1,1]  2*det(5,1,0;6,3,2; 1,1,1] + 3*det[5,2,0; 6,4,2; 1,1,1] 4*det(5,2,1; 6,4,3; 1,1,1] From there I would do the individual det of the 3x3s, but when everything is added up I'm getting a determinant of 0! Did I set things up correctly like on the process of setting up the factor/cofactor method. With the reduction to triangular form, it looks similar to Guassian elimination where I'm trying to get the matrix reduced to upper triangular form. I know that each row swap I make I need to multiply by (1). When I'm done I mulitply the terms outside the matrix to the diagonals. However, I'm still a bit confused, so can anyone explain it a bit better than my textbook? Thanks. 


#2
Mar2204, 09:46 AM

P: 695




#3
Mar2204, 08:52 PM

P: 17

DOH! I shouldn't always rely on the calculator (or at least me inputting wrong values)
Yeah the Det is 0. I still have some trouble with the Triangular form method though. This technique is suppose to be quicker than the Factor/Cofactor technique right? 


#4
Mar2304, 03:36 AM

Sci Advisor
HW Helper
P: 9,396

4x4 Matrix
Yes, a lot quicker. Learn it, it's very useful



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