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In design matters, mechanisms with deformable elements are a step behind those with rigid bars, particularly if dimensional synthesis is considered a fundamental part of mechanism design. For the purposes of this work, a hybrid rigid–flexible four-bar mechanism has been chosen, the input bar being a continuum tendon of constant curvature. The coupler curves are noticeably more complex but offer more possibilities than the classical rigid four-bar counterpart. One of the objectives of this work is to completely characterize the coupler curves of this hybrid rigid–flexible mechanism, determining the number and type of circuits as well as constituent branches. Another important aim is to apply optimization techniques to the dimensional synthesis of path generation. Considerable progress in finding the best design solutions can be obtained if all the acquired knowledge about the coupler curves of this hybrid mechanism is integrated into the optimization algorithm.

We introduce orbital functionals $\int \boldsymbol{\beta} $ simultaneously for each commensurability class of orbital surfaces. They are realized on infinitely dimensional \emph{orbital} divisor spaces spanned by (arithmetic-geodesic real $2$-dimensional) orbital curves on any orbital surface. We discover infinitely many of them on each commensurability class of orbital Picard surfaces, which are real $4$-spaces with cusps and negative constant Kähler-Einstein metric degenerated along an orbital cycle. For a suitable (Heegner) sequence $\int \mathbf{h}_N$, $N \in \mathbb{N}$, of them we investigate the corresponding formal orbital $q$-series $\mathop{\sum}\limits_{N=0}^\infty (\int \mathbf{\mathbf{h}}_N)q^N$. We show that after substitution $q = \re^{2\pi\ri\tau}$ and application to arithmetic orbital curves $\mathbf{\hat{C}}$ on a fixed Picard surface class the series $\mathop{\sum}\limits_{N=0}^{\infty} (\int_{\mathbf{\hat{C}}} \mathbf{\mathbf{h}}_N)\re^{2\pi\ri\tau}$ define modular forms of well-determined fixed weight, level and Nebentypus. The proof needs a new orbital understan-ding of orbital hights introduced in \cite{Ho1} and Mumford-Fulton's rational intersection theory on singular surfaces in Riemann-Roch-Hirzebruch style. It has to be connected with Zeta and Theta functions of hermitian lines, indefinit quaternionic fields and of a matrix algebra along a research marathon over $75$ years represented by Cogdell, Kudla, Hirzebruch, Zagier, Shimura, Schoeneberg and Hecke. Our aim is to open a door to an effective enumerative geometry for complex geodesics on orbital varieties with nice metrics.

We introduce orbital functionals $\int \boldsymbol{\beta} $ simultaneously for each commensurability class of orbital surfaces. They are realized on infinitely dimensional \emph{orbital} divisor spaces spanned by (arithmetic-geodesic real $2$-dimensional) orbital curves on any orbital surface. We discover infinitely many of them on each commensurability class of orbital Picard surfaces, which are real $4$-spaces with cusps and negative constant Kähler-Einstein metric degenerated along an orbital cycle. For a suitable (Heegner) sequence $\int \mathbf{h}_N$, $N \in \mathbb{N}$, of them we investigate the corresponding formal orbital $q$-series $\mathop{\sum}\limits_{N=0}^\infty (\int \mathbf{\mathbf{h}}_N)q^N$. We show that after substitution $q = \re^{2\pi\ri\tau}$ and application to arithmetic orbital curves $\mathbf{\hat{C}}$ on a fixed Picard surface class the series $\mathop{\sum}\limits_{N=0}^{\infty} (\int_{\mathbf{\hat{C}}} \mathbf{\mathbf{h}}_N)\re^{2\pi\ri\tau}$ define modular forms of well-determined fixed weight, level and Nebentypus. The proof needs a new orbital understan-ding of orbital hights introduced in \cite{Ho1} and Mumford-Fulton's rational intersection theory on singular surfaces in Riemann-Roch-Hirzebruch style. It has to be connected with Zeta and Theta functions of hermitian lines, indefinit quaternionic fields and of a matrix algebra along a research marathon over $75$ years represented by Cogdell, Kudla, Hirzebruch, Zagier, Shimura, Schoeneberg and Hecke. Our aim is to open a door to an effective enumerative geometry for complex geodesics on orbital varieties with nice metrics.

Starting from a fixed elliptic curve with complex multiplication we compose lifted quotients of elliptic Jacobi theta functions to abelian functions in higher dimension. In some cases, where complete Picard-Einstein metrics have been discovered on the underlying abelian surface (outside of cusp points), we are able to transform them to Picard modular forms. Basic algebraic relations of basic forms come from different multiplicative decompositions of these abelian functions in simple ones of the same lifted type. In the case of Gauss numbers the constructed basic modular forms define a Baily-Borel embedding in P22. The relations yield explicit homogeneous equations for the Picard modular image surface.

Starting from a fixed elliptic curve with complex multiplication we compose lifted quotients of elliptic Jacobi theta functions to abelian functions in higher dimension. In some cases, where complete Picard-Einstein metrics have been discovered on the underlying abelian surface (outside of cusp points), we are able to transform them to Picard modular forms. Basic algebraic relations of basic forms come from different multiplicative decompositions of these abelian functions in simple ones of the same lifted type. In the case of Gauss numbers the constructed basic modular forms define a Baily-Borel embedding in P22. The relations yield explicit homogeneous equations for the Picard modular image surface.