Encyclopedia > Tensor-classical

Article Content

Classical treatment of tensors

Redirected from Tensor-classical

The following is a component-based "classical" treatment of tensors. See Component-free treatment of tensors for a modern abstract treatment, and Intermediate treatment of tensors for an approach which bridges the two.

The Einstein summation convention is used throughout this page. For help with notation, refer to the table of mathematical symbols.

A tensor is a generalization of the concept of vector and matrices. Tensors allow one to express physical laws in a form that applies to any coordinate system. For this reason, they are used extensively in continuum mechanics and the theory of relativity.

A tensor is an invariant multi-dimensional transformation, that takes forms in one coordinate system into another. It takes the form:

$T^{\left[i_1,i_2,i_3,...i_n\right]}_{\left[j_1,j_2,j_3,...j_n\right]}$

The new coordinate system is represented by being 'barred'($\bar{x}^i$), and the old coordinate system is unbarred($x^i$).

The upper indices [$i_1,i_2,i_3,...i_n$] are the contravariant components, and the lower indices [$j_1,j_2,j_3,...j_n$] are the covariant components.

Contravariant and covariant tensors A contravariant tensor of order 1($T^i$) is defined as:

$\bar{T}^i = T^r\frac{\partial \bar{x}^i}{\partial x^r}$

A covariant tensor of order 1($T_i$) is defined as:

$\bar{T}_i = T_r\frac{\partial x^r}{\partial \bar{x}^i}$

General tensors A multi-order (general) tensor is simply the tensor product of single order tensors:

$T^{\left[i_1,i_2,...i_p\right]}_{\left[j_1,j_2,...j_q\right]} = T^{i_1} \otimes T^{i_2} ... \otimes T^{i_p} \otimes T_{j_1} \otimes T_{j_2} ... \otimes T_{j_p}$

such that:

$\bar{T}^{\left[i_1,i_2,...i_p\right]}_{\left[j_1,j_2,...j_q\right]} = T^{\left[r_1,r_2,...r_p\right]}_{\left[s_1,s_2,...s_q\right]} \frac{\partial \bar{x}^{i_1}}{\partial x^{r_1}} \frac{\partial \bar{x}^{i_2}}{\partial x^{r_2}} ... \frac{\partial \bar{x}^{i_p}}{\partial x^{r_p}} \frac{\partial x^{s_1}}{\partial \bar{x}^{j_1}} \frac{\partial x^{s_2}}{\partial \bar{x}^{j_2}} ... \frac{\partial x^{s_q}}{\partial \bar{x}^{j_q}}$

• Schaum's Outline of Tensor Calculus
• Synge and Schild, Tensor Calculus, Toronto Press: Toronto, 1949

All Wikipedia text is available under the terms of the GNU Free Documentation License

Search Encyclopedia
 Search over one million articles, find something about almost anything!

Featured Article
 Quadratic formula ... x to the quadratic equation $ax^2+bx+c=0$ in terms of the coefficients a, b and c, which are assumed to be real (but see below fo ...