Intuitive explanation for the general determinant formula?


by jjepsuomi
Tags: determinant, linear algebra
jjepsuomi
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#1
Dec18-12, 10:06 AM
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Hello

Could anyone give an intuitive explanation of the determinant? I know mostly what the determinant means and I can calculate it etc. But I have never got any real-world intuitive explanation of the general formula of the determinant?

How is the formula derived? Where does it come from? What I'm essentially asking is: Prove the general formula for calculating the determinant of an n-by-n matrix and explain the meaning of it

Any support = Thank you so much!! =)
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jgens
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Dec18-12, 01:25 PM
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Often the determinant is just defined by the formula:
[tex]\det(a_{ij}) = \sum_{\sigma \in S_n} \mathrm{sgn}(\sigma)a_{1\sigma(1)} \cdots a_{n\sigma(n)}[/tex]
On the other hand, if you define the determinant as the unique alternating multilinear functional [itex]\det:\mathbb{R}^n \times \cdots \times \mathbb{R}^n \rightarrow \mathbb{R}[/itex] (where the product is taken n-times) satisfying [itex]\det(I) = 1[/itex], then you can recover the formula above for the determinant.

Edit: I suppose this is not really an intuitive explanation, but hopefully it helps a little.
micromass
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Dec18-12, 01:36 PM
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A nice and intuitive explanation of the determinant is that it just represents a signed volume.

For example, given the vectors (a,b) and (c,d) in [itex]\mathbb{R}^2[/itex]. Then we can look at the parallelogram formed by (0,0), (a,b), (c,d) and (a+c,b+d). The area of this parallellogram is given by the absolute value of

[tex]det \left(\begin{array}{cc} a & b\\ c & d \end{array}\right)[/tex]

Of course the determinant has a sign as well. This is why we call the determinant the signed volume. That is: if we exchange (a,b) and (c,d), then we get the opposite area. The sign is useful for determining orientation.

tiny-tim
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Dec18-12, 01:36 PM
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Intuitive explanation for the general determinant formula?


hello jjepsuomi! welcome to pf!

i suggest you start in 2D and 3D by considering how the determinant relates the the area of a rectangle to the area of the transformed parallelogram or the volume of a cube to the volume of the transformed parallelepiped,

and then how you'd apply that in n dimensions, and how it affects integration after a transformation
mathwonk
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Dec19-12, 12:26 PM
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saying it is an oriented volume measure implies it should be a multilinear and alternating function. these properties force the formula to be what it is, if you assume the value is 1 on a unit cube. determinants are developed in complete detail starting on p. 62 of these notes.

http://www.math.uga.edu/%7Eroy/4050sum08.pdf


for geometric intuition you might look at the book by david bachmann on geometric approach to differential forms.

http://www.amazon.com/Geometric-Appr...erential+forms


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