Isometry Invariant Shape Recognition of Projectively Perturbed Point Clouds by the Mergegram Extending 0D Persistence

Rigid shapes should be naturally compared up to rigid motion or isometry, which preserves all inter-point distances. The same rigid shape can be often represented by noisy point clouds of different sizes. Hence, the isometry shape recognition problem requires methods that are independent of a cloud size. This paper studies stable-under-noise isometry invariants for the recognition problem stated in the harder form when given clouds can be related by affine or projective transformations. The first contribution is the stability proof for the invariant mergegram, which completely determines a single-linkage dendrogram in general position. The second contribution is the experimental demonstration that the mergegram outperforms other invariants in recognizing isometry classes of point clouds extracted from perturbed shapes in images.

WDVV equations and invariant bi-Hamiltonian formalism

The purpose of the paper is to show that, in low dimensions, the WDVV equations are bi-Hamiltonian. The invariance of the bi-Hamiltonian formalism is proved for N = 3. More examples in higher dimensions show that the result might hold in general. The invariance group of the bi-Hamiltonian pairs that we find for WDVV equations is the group of projective transformations. The significance of projective invariance of WDVV equations is discussed in detail. The computer algebra programs that were used for calculations throughout the paper are provided in a GitHub repository.

Measurements and geometry

The paper is aimed at demonstrating the points of contact between measurements and geometry, which is done by modelling the main elements of the measurement process by the elements of geometry. It is shown that the basic equation for measurements can be established from the expression of projective metric and represents its particular case. Commonly occurring groups of functional transformations of the measured value are listed. Nearly all of them are projective transformations, which have invariants and are useful if greater accuracy of measurements is desired. Some examples are given to demonstrate that real measurement transformations can be dealt with via fractional-linear approximations. It is shown that basic metrological and geometrical categories are related, and a concept of seeing a multitude of physical values as elements of an abstract geometric space is introduced. A system of units can be reasonably used as the basis of this space. Two tensors are introduced in the space. One of them (the affinor) describes the interactions within the physical object, the other (the metric tensor) establishes the summation rule on account of the random nature of components.

Kahlerian manifolds related in H-projective recurrent curvature killing vector fields with vectorial fields

Izumi and Kazanari [2], has calculated and defined on infinitesimal holomorphically projective transformations in compact Kaehlerian manifolds. Also, Malave Guzman [3], has been studied transformations holomorphic ammeters projective equivalentes. After that, Negi [5], have studied and considered some problems concerning Pseudo-analytic vectors on Pseudo-Kaehlerian Manifolds. Again, Negi, et. al. [6],has defined and obtained an analytic HP-transformation in almost Kaehlerian spaces. In this paper we have measured and calculated a Kahlerian manifolds related in H-projective recurrent curvature killing vector fields with vectorial fields and their holomorphic propertiesEinsteinian and the constant curvature manifoldsare established.Kaehlerian holomorphically projective recurrent curvature manifolds with almost complex structures by using the geometrical properties of the harmonic and scalar curvatures calculated overkilling vectorial fieldsare obtained

Differentiability of projective transformations in dimension 2

It is proven by elementary methods that in dimension 2, every locally injective continuous map, sending the curves of a Ck-spray to curves of another Ck-spray as oriented point sets, is a Ck-diffeomorphism. This extends the result [1] for dimension three and higher from 1965.