double precision function kutl_vertex_err_project(Vvtx, eta)
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*
*  Returns the vertex error along a specified direction.
*
*  Input Parameters:
*  Vvtx(3,3)      double precision array
*                 Vertex covariance matrix
*
*  eta(3)         double precision array
*                 Direction cosines defining the direction along which
*                 the error is evaluated. They do not have to be
*                 normalized to 1.
*
*  Output Parameters:
*
*  Return Value:
*                 Error of vertex along projection.
*  Other routines:
*
*  Notes:
*
*  Author:   Paul Avery      Created:  Tue Sep 23 23:10:11 EDT 1997
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*  Major revisions:
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