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The numbers eiej arranged into a matrix would form a symmetric matrix (a matrix equal to its own transpose) due to the symmetry in the dot products, in fact it is the metric tensor g. By contrast eiej or eiej do not form symmetric matrices in general, as displayed above. WGPbGaamOAaaqabaGccqGH9aqpcaWGbbWaaSbaaSqaaiaadMgacaWG
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When you have a Kronecker delta ij and one of the indices is repeated (say i), then you simplify it by replacing the other iindex on that side of the equation by jand removing
Is there anything called Shallow Learning. ijk
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For the mechanical example above for the tangential velocity of a rigid body, given by v = x, this can be rewritten as v = x where is the tensor corresponding to the pseudovector : For an example in electromagnetism, while the electric field E is a vector field, the magnetic field B is a pseudovector field.
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The relationship between the . 3
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For context, this is discussed whilst going over an introduction to the moment of inertia tensor.
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In the same manner the permutation tensor allows us to to write the .
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For the above cases:[1][2].
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Hence the components reduce to direction cosines between the xi and xj axes: where ij and ji are the angles between the xi and xj axes.
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Conventions
e k ^ _ (btw: that's an awful lot of indications it's a vector) just means the k 'th unit vector, with that in mind try to calculate the dot product again. aacMcaaaGaeyicI48aaSbaaSqaaiaadMgacaWGWbGaamyCaaqabaGc
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And the dot product of two vector quantity V and F is, In a Cartesian basis, the gradient of a scalar () and the divergence of a vector D can be variously written as, .
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Is it possible? [emailprotected]@[emailprotected]@+=
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Also there's a relation with the Dirac Delta, but I think what you wanted to know is that. [emailprotected]@
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Note that $\cos(0^\circ)=1$. x
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II.A Dot Products of Vectors. Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. a
Vector operations expressed using
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component matrices of A, B and C. The Kronecker
tangent to spherical coordinates), Cartesian tensors may provide considerable simplification for applications in which rotations of rectilinear coordinate axes suffice. k
when we have a coordinate vector in a column vector representation: A row vector representation is also legitimate, although in the context of general curvilinear coordinate systems the row and column vector representations are used separately for specific reasons see Einstein notation and covariance and contravariance of vectors for why.
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1 Answer Sorted by: 1 You have defined a new inner product. feaagKart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn
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efficiently and clearly using index
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Cartesian tensors may be used with any Euclidean space, or more technically, any finite-dimensional vector space over the field of real numbers that has an inner product.
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Sometimes general curvilinear coordinates are convenient, as in high-deformation continuum mechanics, or even necessary, as in general relativity.
is and contains sums of of the products ,; is and contains all products .
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which one to use in this conversation? b
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Tensors are defined as quantities which transform in a certain way under linear transformations of coordinates.
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As for the curl of a vector field A, this can be defined as a pseudovector field by means of the symbol: which is only valid in three dimensions, or an antisymmetric tensor field of second order via antisymmetrization of indices, indicated by delimiting the antisymmetrized indices by square brackets (see Ricci calculus): which is valid in any number of dimensions. e9pgea0dXdar=Jb9hs0dXdbPYxe9vr0=vr0=vqpWqaaeaabiGaciaa
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The transformation is a passive transformation, since the coordinates are changed and not the physical system.
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The matrix forms provide a clear display of the components, while the index form allows easier tensor-algebraic manipulation of the formulae in a compact manner. of a tensor and a vector
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We also occasionally make use of the alternating (or Levi-Civita) symbol , which is defined such that (5) to see that, {
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j Start with an x,y,z coordinate system and ask, "What are \( {\partial x \over \partial x} \), The answers are simple: 1, 0, and 0.
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The special tensors, Kronecker delta and Levi-Civita symbol, are introduced and used in calculating the dot and cross products of vectors.
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Ah ok, thanks. [emailprotected]@.
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(See also below for more on the dot and cross products). [emailprotected]@[emailprotected]@+=
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More precisely, for a real vector space, an inner product satisfies the following four properties. a
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The function, matrix, and index notations all mean the same thing.
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Exactly the same transformation rules apply to any vector a, not only the position vector.
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A second-order tensor T which takes in a vector u of some magnitude and direction will return a vector v; of a different magnitude and in a different direction to u, in general.
The most familiar coordinate systems are the two-dimensional and three-dimensional Cartesian coordinate systems. feaagKart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn
The dot product of two vectors AB in this notation is AB = A 1B 1 + A 2B 2 + A 3B 3 = X3 i=1 A iB i = X3 i=1 X3 j=1 A iB j ij: . i
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From my understanding this is equal to
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which is intuitive, since the dot product of two vectors is a single scalar independent of any coordinates. dMgacaWGQbaabeaakiaadkeadaWgaaWcbaGaamyAaiaadUgaaeqaaO
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The Kronecker delta. j
Theoretical Approaches to crack large files encrypted with AES.
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Therefore, $$e_i\cdot e_j=\cos\angle(e_i,e_j)=\cos 90^\circ=0=\delta_{ij}.$$.
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Let
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Theith component of the cross produce of two vectorsABbecomes 33 (AB)iXX =ijkAjBk.
The Kronecker delta, dij is defined as: dij =0ifij1if i=jwhere i and j are subscripts As you can see, the Kronecker delta nicely summarizes the rules for computing dot products of orthogonal unit vectors; if the twovectors have the same subscript, meaning they are in the same direction, their dot product is one. aaqabaGccqGHRaWkcaWGtbWaaSbaaSqaaiaaigdacaaIYaaabeaaki
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and the explicit matrix equations in 3d are: As with all linear transformations, L depends on the basis chosen. \left( ij
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The four-vectors of special relativity require a slight generalization of indices to not just subscripts but also superscripts. caGaaeqabaGadeaadaaakqaabeqaaiabeU7aSjabg2da9iGacsgaca
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I would take $a\cdot b=\cos\angle(a,b)$ to be essentially the.
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Use the Kronecker product to construct block matrices. gadaWgaaWcbaGaaGOmaaqabaGccaWGIbWaaSbaaSqaaiaaikdaaeqa
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of two tensors
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March 22, 2020 This note is a brief description of the matrix Kronecker product and matrix stack algebraic operators.
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Each basis vector ei points along the positive xi axis, with the basis being orthonormal.
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Ask Question Asked 2 years, 11 months ago.
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An inner product is a generalization of the dot product. [emailprotected]@[emailprotected]@+=
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How to show errors in nested JSON in a REST API?
b can be written as a ib j ij = a ib i. m
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Other identities can be formed from the tensor and pseudotensor, a notable and very useful identity is one that converts two Levi-Civita symbols adjacently contracted over two indices into an antisymmetrized combination of Kronecker deltas: The index forms of the dot and cross products, together with this identity, greatly facilitate the manipulation and derivation of other identities in vector calculus and algebra, which in turn are used extensively in physics and engineering.
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For the tensor relating a vector to a vector, the vectors and tensors throughout the equation all belong to the same coordinate system and basis. =
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Let T = T(r, t) denote a second order tensor field, again dependent on the position vector r and time t. For instance, the gradient of a vector field in two equivalent notations ("dyadic" and "tensor", respectively) is: which is a vector field. Semantics of the `:` (colon) function in Bash when used in a pipe? rev2023.6.2.43474. For perpendicular pairs we have
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can just apply the usual chain and product rules of differentiation, r
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In mathematics, especially the usage of linear algebra in mathematical physics, Einstein notation (also known as the Einstein summation convention or Einstein summation notation) is a notational convention that implies summation over a set of indexed terms in a formula, thus achieving brevity.
When vectors and tensors are written without reference to components, and indices are not used, sometimes a dot is placed where summations over indices (known as tensor contractions) are taken. igdaaeqaaOGaamOyamaaBaaaleaacaaIXaaabeaakiabgUcaRiaadg
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Free indices on each term of an
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Here, the orientation is fixed by 123 = +1, for a right-handed system. 1+
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In the change of coordinates, L is a matrix, used to relate two rectangular coordinate systems with orthonormal bases together.
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Given column vectorsvandw, we have seen that the dot productv wis the same as the matrix multiplicationvTw. Yxir=Jbba9q8aq0=yq=He9q8qqQ8frFve9Fve9Ff0dmeaabaqaciGa
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components of A in this basis by
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Kronecker delta is also a function that has only integer values defined between two integers (in most cases, two natural numbers). gives the transformation law of an order-2 tensor. In each case, the order of the gradient and vector field components should not be interchanged as this would result in a different differential operator: which could act on scalar or vector fields. ij
denotes three components of a vector
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d
caGaaeqabaGadeaadaaakeaacaaMc8UaaGPaVlaaykW7daqadaqaai
i
Kronecker delta ij - is a small greek letter delta, which yields either 1 or 0, depending on which values its two indices iand jtake on. ij
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33
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+
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}
i1
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$\begingroup$ maybe for the Kronecker delta is still true, but I admit that there are much less involved ways to prove that thing $\endgroup$ - Francesco Bernardini. =
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are the components of the stress and strain
vectors or tensors, summation is implied over the repeated index. Thus, =
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Recalling that any entity multiplied by the Kronecker delta will have its index exchanged with the free index of the Kronecker delta, we obtain: Finally, given that repeated indices represent a sum over those indices, we realize that the dot product is a scalar that is the sum of each component of one vector . Stack Exchange network consists of 181 Q&A communities including Stack Overflow, the largest, most trusted online community for developers to learn, share their knowledge, and build their careers. b
=
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123
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S
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(
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={
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+
on Cartesian components of vectors and tensors may be expressed very
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be a second basis, and denote the components
where
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on Cartesian components of vectors and tensors may be expressed very
x be a (three dimensional) vector
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A
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caGaaeqabaGadeaadaaakeaacaWHbbGaeyypa0JaaCOqamaaCaaale
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back into the equation given for. hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr
n
gadaWgaaWcbaGaamOAaaqabaGccaaMc8UaaGPaVlaaykW7cqGHuhY2
can be deduced by noting that
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aSbaaSqaaiaadUgaaeqaaOGaamyyamaaBaaaleaacaWGQbaabeaaki
k
hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr
31
x
be vector fields, in which all scalar and vector fields are functions of the position vector r and time t. The gradient operator in Cartesian coordinates is given by: and in index notation, this is usually abbreviated in various ways: This operator acts on a scalar field to obtain the vector field directed in the maximum rate of increase of : The index notation for the dot and cross products carries over to the differential operators of vector calculus.
[emailprotected]@, You can also think of
A Cartesian basis does not exist unless the vector space has a positive-definite metric, and thus cannot be used in relativistic contexts.
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ij
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feaagKart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn
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=
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=0
The result of the dot product is a number, not a vector. jm
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2
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hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr
C=AB
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=
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aiaadUgacaWGQbaabeaakiaacYcacaaMc8UaaGPaVlaaykW7caaMc8
[emailprotected]@[emailprotected]@+=
0=vqpWqaaeaabiGaciaacaqabeaadaqaaqaaaOabaeqabaGaeqiTdq
ik
m
More generally, whether or not T is a tensor product of two vectors, it is always a linear combination of the basis tensors with coordinates Txx, Txy, , Tzz: Second-order tensors occur naturally in physics and engineering when physical quantities have directional dependence in the system, often in a "stimulus-response" way. k
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The Cartesian labels are replaced by tensor indices in the basis vectors ex e1, ey e2, ez e3 and coordinates ax a1, ay a2, az a3.
13
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caWGRbGaamiBaaqabaaaaOGaeyypa0JaeqiTdq2aaSbaaSqaaiaadM
aIZaaabeaakiabg2da9iaaigdacaaMc8UaaGPaVlaaykW7caaMc8Ua
[emailprotected]@[emailprotected]@+=
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322
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In general, ij is not equal to ji, because for example 12 and 21 are two different angles. 111
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As I said, we build the Kronecker Delta to reflect the usual inner product completely. 3
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P
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ac
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=
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4rNCHbGeaGqiFKI8=feu0dXdh9vqqj=hEeeu0xXdbba9frFj0=OqFf
feaagKart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn
A
[emailprotected]@[emailprotected]@+=
A
feaagKart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn
221
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aaleaacaWGPbGaeyypa0JaaGymaaqaaiaaiodaa0GaeyyeIuoakiab
Let
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= 12
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k
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a
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=
+
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feaagKart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn
31
2.2 Index Notation for Vector and Tensor Operations. S
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i
Throughout, when referring to Cartesian coordinates in three dimensions, a right-handed system is assumed and this is much more common than a left-handed system in practice, see orientation (vector space) for details. For Cartesian tensors of order 1, a Cartesian vector a can be written algebraically as a linear combination of the basis vectors ex, ey, ez: where the coordinates of the vector with respect to the Cartesian basis are denoted ax, ay, az. aaqabaGccqGH9aqpcqGHiiIZdaWgaaWcbaGaaGymaiaaikdacaaIXa
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Convention: Lower case Latin subscripts (i, j, k) have the range
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Vector calculus identities can be derived in a similar way to those of vector dot and cross products and combinations.
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It is common and helpful to display the basis vectors as column vectors. aaykW7caaMc8UaaGPaVlaaykW7caaIZaGaaiilaiaaigdacaGGSaGa
A left-handed system would fix 123 = 1 or equivalently 321 = +1. j
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I run the physics website universaldenker.org More about me: https://en.universaldenker.org/avatars/fufaevUseful links:----------------------------------- Playlists: https://youtube.com/c/universaldenker-physics/playlists Online formulary: https://en.universaldenker.org/formulas Exercises with solutions: https://en.universaldenker.org/exercises Free physics images: https://en.universaldenker.org/illustrations Physics questions: https://en.universaldenker.org/questions#universaldenkerYou may reuse the videos for your own purposes. n
expressed using index notation.
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cross products and dot products of vectors to see how this is done), (
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A
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There is a (partially mnemonical) correspondence between index positions attached to L and in the partial derivative: i at the top and j at the bottom, in each case, although for Cartesian tensors the indices can be lowered. 0=vqpWqaaeaabiGaciaacaqabeaadaqaaqaaaOqaaiaahogacqGH9a
by a Kronecker delta has the effect of switching indices) so, (
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aadUgaaeqaaOGaeyypa0JaaG4maaqaaiaadggadaWgaaWcbaGaamyA
strain relation,
We use copious amounts of dot products, so it is convenient to define the Kronecker delta : (3) Clearly, (4) The alternating symbol. abes7aKnaaBaaaleaacaWGQbGaamyBaaqabaGccqaH0oazdaWgaaWc
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Here, the role of the Kronecker delta is to take two coordinates that were different and make them the same - Ben Grossmann Nov 12, 2020 at 18:04 1
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When one of the components is a vector of all 1s, then "forming a block matrix" is the same as concatenation. 11
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[2] Let c be a vector, a be a pseudovector, b be another vector, and T be a second order tensor such that: As the cross product is linear in a and b, the components of T can be found by inspection, and they are: so the pseudovector a can be written as an antisymmetric tensor.
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1 Answer Sorted by: 0 This has nothing to do with the Kronecker Delta per se.
The Levi-Civita symbol entries can be represented by the Cartesian basis: which geometrically corresponds to the volume of a cube spanned by the orthonormal basis vectors, with sign indicating orientation (and not a "positive or negative volume"). [emailprotected]@, Product
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tensor. Let
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dummy indices may be changed without altering the meaning of an expression,
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I think what was meant (as eyeballfrog mentioned in the comments), is that the inner product of the space V is the dot product when the basis is orthonormal with respect to that inner product. S
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Modified 2 years, 11 months ago.
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Cartesian tensors are as in tensor algebra, but Euclidean structure of and restriction of the basis brings some simplifications compared to the general theory.
the same expression on the right hand side takes the same form in higher dimensions (see below).
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This means $\angle(e_i,e_j)=90^\circ$ and $\cos 90^\circ=0$. [emailprotected]@, for
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}
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: The position vector x in
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and let S be a second order
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Scalar product with Kronecker delta Here , and are three basis vectors . T
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of Basis. Let a be a vector.
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A dyadic tensor T is an order-2 tensor formed by the tensor product of two Cartesian vectors a and b, written T = a b. Analogous to vectors, it can be written as a linear combination of the tensor basis ex ex exx, ex ey exy, , ez ez ezz (the right-hand side of each identity is only an abbreviation, nothing more): Representing each basis tensor as a matrix: then T can be represented more systematically as a matrix: See matrix multiplication for the notational correspondence between matrices and the dot and tensor products. j
x denote the
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In mathematics, the Kronecker delta (named after Leopold Kronecker) is a function of two variables, usually just non-negative integers. i
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mk
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v8qqaqFD0xXdHaVhbbf9v8qqaqFr0xc9pk0xbba9q8WqFfea0=yr0R
B
1
caWGvbWaaSbaaSqaaiaadUgaaeqaaOGaamyyamaaBaaaleaacaWGRb
eyypa0JaaGymaaqaaiaaiodaa0GaeyyeIuoakiaaykW7caaMc8UaaG
index notation, we would express x and
ij
n
The use of second-order tensors are the minimum to describe changes in magnitudes and directions of vectors, as the dot product of two vectors is always a scalar, while the cross product of two vectors is always a pseudovector perpendicular to the plane defined by the vectors, so these products of vectors alone cannot obtain a new vector of any magnitude in any direction. A
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