# Invariants of Quadratic Differential Forms

University Press, 1908 - Differential forms - 90 pages

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Page 64 - It appears that, if the surfaces <f, const. can form part of a triply orthogonal system, <£ must satisfy a differential equation of the third order*, and the other two families of surfaces are then determinate. As the method of determining this equation of the third order is an instructive example of the use and advantages of differential invariants, and in particular of covariant differentiation, we give it in detail. Let u, v, w be three families that form a triply orthogonal system, then...
Page 30 - Another group is given by all the transformations of the form x' = ax + by, y' -cx + dy, where a, b, c, d, are arbitrary.
Page 18 - I t,... of the algebraic forms F, Gt,... are a complete system of relative' differential invariants for the quadratic differential form F, and if under any transformation such an invariant I becomes kl, then k is some power of the Jacobian of the transformation. If we take account of differential invariants which involve the magnitudes dx themselves...
Page 14 - F' is possible. We thus have the important result : The necessary and sufficient conditions in order that it shall be possible to transform a quadratic form F into another quadratic form <>x F...
Page 53 - ... an example of this has already been given in the case of the rolls for the year 19 Edward I.
Page 67 - ... thus associated a direction with each point in the manifold, and, if we start from a given point and proceed always in the direction associated with the point reached, we finally obtain a curve in the manifold. Hence the equations given above define a congruence of curves in the manifold, such that there is one and only one curve through each point of the manifold. Let /* define another such congruence, then the cosine of the angle between two intersecting curves, one belonging to the congruence...
Page 58 - Gdv2 = 0, that is to say df = 0. The curves are hence such that the distance between any two points on one of them, measured along that curve, is zero. Consider the more general case of A <£=/(<£). Let the curves...
Page 78 - This vector possesses the properties (1) It is identically zero if [n] is geodesic. (2) Its projection on the plane tangent to the lines i and n is equal to the curvature of the projection of the line n on the same plane. (3) It is normal to the line n. For these reasons y is called the geodesic curvature of the line n, and the congruence p is called that of the lines of geodesic curvature of [n].
Page 37 - A=l and it is easy to prove that if one set of functions u is given, the most general possible set is given by performing a general orthogonal transformation and a translation on the set u. The problem in this particular case is therefore seen to separate into two parts...
Page 33 - ... so as to include the transformation equations for the new variables introduced and their derivatives, and our problem is to determine all the invariants of this extended group. To do this it is necessary to obtain the infinitesimal transformations of the group, and from these we obtain a complete system of linear differential equations the solutions of which are the invariants. 34. The case of two independent variables. As a first case we consider a quadratic form in two variables x, y. Let x'...