A fourth-order tensor relates two second-order tensors. Matrix notation of such relations is only possible, when the 9 components of the second-order tensor are . space equipped with coefficients taken from some good operator algebra. In this paper we introduce, using only the non-matricial language, both the classical (Grothendieck) projective tensor product of normed spaces. then the quotient vector space S/J may be endowed with a matricial ordering through .. By linear algebra, the restriction of σ to the algebraic tensor product is a.

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A single convention can be somewhat standard throughout a single field that commonly uses matrix calculus e. To convert to normal derivative form, first convert it to one of the following canonical forms, and then use these identities:. In the latter case, the product rule can’t quite be applied directly, either, but the equivalent can be done with a bit more work using the differential identities. Moreover, we have used bold letters to lagebra vectors and bold capital letters for matrices.

As noted above, cases where vector and matrix denominators are written in transpose notation are equivalent to numerator layout with the denominators written without the transpose.

A is not a function of XX is non-square, A is non-symmetric. A is not a function of x A is symmetric.

### [math/] Tensor Products in Quantum Functional Analysis: the Non-Matricial Approach

For this reason, in this subsection maatricial consider only how one can write the derivative of a matrix by another matrix. In cases involving matrices where it makes sense, we give numerator-layout and mixed-layout results. In mathematicsmatrix calculus is a specialized notation for doing multivariable calculusespecially over spaces of matrices. Notice that as we consider higher numbers of components in each of the independent and dependent variables we can be left with a very large number of possibilities.

An element of M 1,1 is a scalar, denoted with lowercase italic typeface: It is important to realize the following:. As for vectors, the other two types of higher matrix derivatives can be seen as applications of the derivative of a matrix by a matrix by using a matrix with one column in the correct place. Uses the Hessian transpose to Jacobian definition of vector and matrix derivatives. Matrix theory Linear algebra Multivariable calculus.

Thus, either the results should be transposed at the end or the denominator layout or mixed layout should be used. All functions are assumed to be of differentiability class C 1 unless otherwise noted. Differentiation notation Second derivative Third derivative Change of variables Implicit differentiation Related rates Taylor’s theorem. When taking derivatives with an aggregate vector or matrix denominator in order to find a maximum or minimum of the aggregate, it should be kept in mind that using numerator layout will produce results that are transposed with respect to the aggregate.

The next two introductory sections use the numerator layout convention simply for the purposes of convenience, to avoid overly complicating the discussion. It is the gradient matrix, in particular, that finds many uses in minimization problems in estimation theoryparticularly in the mattricial of the Kalman filter algorithm, which is of great importance in the field.

Using numerator-layout notation, we have: As a result, the following layouts can often be found:. In that case the scalar algebrz be a function of each of the independent variables in the matrix.

X T denotes matrix transposetr X is the traceand det X or X is the mwtricial. As is the case in general for partial derivativessome formulae may extend under weaker analytic conditions than the existence of the derivative as approximating linear mapping.

The section on layout conventions discusses this issue in greater detail. In the following three sections we will define each one of these derivatives and relate them to other branches of mathematics. Each different situation will lead to a different set of rules, or a separate calculususing the broader sense of the term.

Further see Derivative of the exponential map. The directional derivative of a scalar function f x of the space vector x in the direction of the unit vector u is defined using the gradient as follows. The chain rule applies in some of the cases, but unfortunately does not apply in matrix-by-scalar derivatives or scalar-by-matrix derivatives in the latter case, mostly involving the trace operator applied to matrices. The matrix derivative is a convenient notation for keeping track of partial derivatives for doing calculations.

Some authors use different conventions.

Fundamental theorem Limits of functions Continuity Mean value theorem Rolle’s theorem. Keep in mind that various authors use different combinations of numerator and denominator layouts for different types of derivatives, and there is no guarantee that an author will consistently use either numerator or denominator layout for all types.

This book uses a mixed layout, i. Note that a matrix can be considered a tensor of rank two. However, these derivatives are most naturally organized in a tensor of rank higher than 2, so that they do not fit neatly into a matrix.

## Matrix calculus

Also in analog with vector calculusthe directional derivative of a scalar f X of a matrix X in the direction of matrix Y is given by. Retrieved from ” https: Archived from the original on 2 March To help make sense of all the identities below, keep in mind the most important rules: Also, Einstein notation can be very useful in proving the identities presented here see section on differentiation as an alternative to typical element notation, which can become cumbersome when the explicit sums are carried around.

Notice here that y: Although there are largely two consistent conventions, some authors find tensodial convenient to mix the two conventions in forms that are discussed below.

The tensor index notation with its Einstein summation convention is very similar to the matrix calculus, except one writes only a single component at a time. The fundamental issue is that the derivative of a vector with respect to a vector, i. Matrix differential calculus is used in statistics, particularly for the statistical analysis of multivariate distributionsespecially the multivariate normal distribution and other elliptical distributions.

Example Simple examples of this include the velocity vector in Euclidean spacewhich is the tangent vector of the position vector considered as a function of time. That is, sometimes different conventions are used in different contexts within the same book or paper. Linear algebra and its applications 2nd ed.

Using denominator-layout notation, we have: Notice that we could also talk about the derivative of a vector with respect to a matrix, or any of the other maticial cells in our tebsorial.

Authors of both groups often write as though their specific convention were standard.