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Dual basis

  • Page ID
    17553
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    The dual basis is a basis associated to the basis of a vector space. In three-dimensional space, it is isomorphous to the basis of the reciprocal lattice. It is mathematically defined as follows:

    Given a basis of n vectors ei spanning the direct space En, and a vector x = x i ei, let us consider the n quantities defined by the scalar products of x with the basis vectors, ei:

    xi = x . ei = x j ej . ei = x j gji,

    where the gji 's are the doubly covariant components of the metric tensor.

    By solving these equations in terms of x j, one gets:

    x j = xi gij

    where the matrix of the gij 's is inverse of that of the gij 's (gikgjk = δij). The development of vector x with respect to basis vectors ei can now also be written:

    x = x i ei = xi gij ej

    The set of n vectors ei = gij ej that span the space En forms a basis since vector x can be written:

    x = xi ei

    This basis is the dual basis and the n quantities xi defined above are the coordinates of x with respect to the dual basis. In a similar way one can express the direct basis vectors in terms of the dual basis vectors:

    ei = gij ej

    The scalar products of the basis vectors of the dual and direct bases are:

    gij = ei . ej = gik ek . ej = gikgjk = δij.

    One has therefore, since the matrices gik and gij are inverse:

    gij = ei . ej = δij.

    These relations show that the dual basis vectors satisfy the definition conditions of the reciprocal vectors. In a three-dimensional space the dual basis and the basis of reciprocal space are identical.


    Dual basis is shared under a CC BY-NC-SA 4.0 license and was authored, remixed, and/or curated by Online Dictionary of Crystallography.