Lens (ERG Volume)

Lens (ERG Volume)

GRG Lens — Points • Dual Surface • ERG Volume • Smooth (C²)

Abstract. A lens is the envelope of two surfaces (front $S_1$, back $S_2$) with a shared rim. At resolution $\varepsilon$, the local step obeys:

$$ h(u,v) \;\le\; 2\,\sqrt{\frac{\varepsilon}{\kappa_{\max}(u,v)}}, $$

We build the closed solid and compute the ERG volume, then apply Smooth$_\varepsilon$ with $C^{2}$ continuity to avoid optical edges.

1) Definitions (curvatures & adaptive step)

  • Principal curvatures $(\kappa_1,\kappa_2)$; $\kappa_{\max}=\max(|\kappa_1|,|\kappa_2|)$.
  • Local step $h(u,v)$: imposed by $2\sqrt{\varepsilon/\kappa_{\max}}$.
  • Perfect at scale $\varepsilon$: geometric deviation $\le \varepsilon$ on the whole lens.

Axisymmetric case $z=f(r)$

$$ \kappa_{\text{mer}}=\frac{f''(r)}{\bigl(1+f'(r)^{2}\bigr)^{3/2}}, \qquad \kappa_{\text{circ}}=\frac{f'(r)}{r\,\sqrt{1+f'(r)^{2}}}, \qquad \kappa_{\max}=\max\!\bigl(|\kappa_{\text{mer}}|,|\kappa_{\text{circ}}|\bigr). $$

2) Points → Dual surface → ERG volume

2.1 Points (adaptive radial–angular grid)

Sample $S_1$ and $S_2$ with $\Delta r$, $\Delta \theta$ such that local geodesic spacing never exceeds $h(u,v)$. Density increases where $\kappa_{\max}$ is higher (small radii or high-curvature regions).

2.2 Surfaces and closure

Build two coherent meshes $S_1, S_2$ and close with a thin lateral ring (cylindrical rim) to obtain a closed, oriented solid.

2.3 ERG volume

Tetrahedra method (as for the sphere) on the closed mesh:

$$ V_{\mathrm{ERG}}=\frac{1}{6}\sum_{\triangle ijk}\bigl((p_i\times p_j)\cdot p_k\bigr). $$

If axisymmetric, cylindrical shells give a consistent Riemann sum:

$$ V_{\mathrm{ERG}}\;\approx\; 2\pi\sum_{k}\; t(r_k)\, r_k\,\Delta r, \qquad t(r)=z_1(r)-z_2(r), $$

which matches the tetrahedra estimate with $O(h^{2})$ error when the sampling bound is enforced.

3) Smooth$_{\varepsilon}$ for optics (C² continuity)

Goal: remove micro-faceting and guarantee surface and derivative continuity ($C^{2}$) for stable normals and curvature.

  1. Local MLS/RBF fit (degree $\ge 2$) on a radius $\rho\in[h,2h]$ for each face.
  2. Resample vertices on the smoothed patches; deviation $\le \varepsilon/2$.
  3. Normal filtering along geodesic neighborhoods, bandwidth $\propto \varepsilon$.
  4. Optical check: angular variation of normals consistent with expected faceting and no edges (no $C^{1}$ discontinuities).
  5. Topology check: no self-intersections after smoothing.

4) Algorithm (concise)

input: surfaces S1, S2 (or z1=f1(r), z2=f2(r)), ε
for each face S∈{S1, S2}:
    compute κ_max(u,v)  # or, for revolution, κ_mer(r), κ_circ(r)
    set h(u,v) ← 2*sqrt(ε/κ_max(u,v))
    generate adaptive grid (Δr, Δθ) satisfying h

T ← triangulate(S1) ∪ triangulate(S2) ∪ cylindrical_rim
orient(T)
A ← sum_areas(T)
V_ERG ← tetra_volume(T)

if optical requirements:
    T' ← smooth_MLS_RBF_C2(T) with deviation ≤ ε/2
    check_normals(T')          # continuity & angular variation
    check_self_intersections(T')
output: (closed mesh T', A, V_ERG, normals)

5) Checks & validation

  • Hausdorff (ideal ↔ mesh) $\le \varepsilon$.
  • $C^{2}$ continuity after smoothing (tests on numerical derivatives of patches).
  • Triangle quality and no self-intersections.
  • (Optional) qualitative optical test: no “steps”.

6) Why it matters

Lenses require $C^{2}$ continuity: even tiny edges degrade refraction. GRG adaptive sampling densifies where needed; Smooth$_\varepsilon$ controls deviation. The result is a lens “perfect at the chosen resolution”, with validated ERG volume.

7) Figures (inline SVG)

Meridional section: z1(r), z2(r) and cylindrical rim Two smooth profiles forming a biconvex lens; the rim is closed with a short cylinder to make a watertight solid. z r z₁ z₂ rim
L2 — Meridional section (profiles $z_1$, $z_2$) and rim closure.
Adaptive step h(u,v) from κmax Radial density sketch: smaller step near high curvature regions; circles represent iso-radius samples with varying spacing.
L1 — Density map driven by $\kappa_{\max}$: smaller $h$ where curvature is higher.

8) FAQ

How do I choose $\varepsilon$ for optics?
Start from the required form tolerance (e.g., $\lambda/10$ or microns) and translate it into a geometric deviation limit.

Does smoothing alter dioptric power?
No, if capped at $\varepsilon/2$ and validated with deviation maps and derivative checks.

What about the rim?
Close with a coherent ring: no sharp or inverted edges; enforce correct orientation.

ERG Quick Calculator ERG grid icon Concentric arcs with dyadic ticks representing ERG refinement.

This compact tool computes the quarter-sampling step Δu and the grid size K from the dyadic level b, previews the uk values, and exports the grid to CSV.

Inputs

  • Dyadic level b ∈ ℕ≥0 (recommended range: 0–18)
  • Optional: recent estimates V2b-1 and V2b to check the dyadic stopping rule
\[ \Delta u \;=\; 2^{-(b+2)}, \qquad K \;=\; \left\lfloor \frac{1}{\Delta u} \right\rfloor \;=\; 2^{\,b+2}. \]
\[ \text{Stop if}\quad \bigl|V_{2^{b}} - V_{2^{b-1}}\bigr| \le \varepsilon. \]

Calculator

Results

  • Δu = — (exact: —)
  • K = — (i.e., number of grid points)
  • N = — (turns-first level, N = 2b)
Preview of u-grid uk = k · Δu

First 8: —

Last 8: —

—

Practical checklist

  • Use dyadic refinement: increase b until the dyadic difference falls below ε.
  • Quarter-sampling is assumed: Δu = 2-(b+2).
  • Grid is deterministic; CSV can be versioned for reproducibility.
ERG volume

ERG volume

GRG Sphere — Points • Surface • ERG Volume • Smooth

Abstract. A sphere of radius $R$ is generated as a quasi-uniform point set. With sampling step:

$$ h_{\max}(\kappa,\varepsilon)\;=\;2\sqrt{\frac{\varepsilon}{\kappa}}, \qquad \kappa=\frac{1}{R}, $$

the reconstructed surface is perfect at scale $\varepsilon$ (geometric error $\le \varepsilon$); area and ERG volume converge with $O(h^2)$ error.

1) Definitions

  • Resolution $\varepsilon$: admissible indistinguishability threshold.
  • Step $h$: distance between nearby surface samples.
  • Curvature $\kappa$: for a sphere, $\kappa = 1/R$.
  • Perfect at scale $\varepsilon$: Hausdorff distance (ideal ↔ reconstructed) $\le \varepsilon$.

Geometric reminder (sagitta of an arc of radius $R$):

$$ s \;\approx\; \frac{h^{2}}{8R} \;=\; \frac{\kappa h^{2}}{8} $$
$$ \Rightarrow\quad h_{\max} \;=\; 2\sqrt{\frac{\varepsilon}{\kappa}} \;=\; 2\sqrt{\varepsilon R}. $$

2) Points → Surface → ERG volume

2.1 Points (quasi-uniform sampling)

  • Spherical Fibonacci lattice: simple and isotropic.
  • Icosphere (subdivided icosahedron): regular connectivity.

Point count (triangles near-equilateral, area $(\sqrt{3}/2)\,h^2$):

$$ N \;\approx\; \frac{4\pi R^{2}}{(\sqrt{3}/2)\,h^{2}} \;=\; \frac{2\pi}{\sqrt{3}}\,\frac{R}{\varepsilon}. $$

It grows linearly with $R/\varepsilon$.

2.2 Surface (closed, oriented mesh)

Triangulate coherently on the spherical manifold. Face normal: $\mathbf{n}_f \propto (p_j-p_i)\times(p_k-p_i)$.

Discrete area:

$$ A \;=\; \sum_{\triangle ijk} \frac{1}{2}\,\big\|\, (p_j-p_i)\times(p_k-p_i)\, \big\|. $$

2.3 ERG volume (from closed surface)

With an oriented closed mesh (tetrahedra w.r.t. the origin):

$$ V_{\mathrm{ERG}} \;=\; \frac{1}{6}\sum_{\triangle ijk}\big((p_i\times p_j)\cdot p_k\big). $$

Convergence: $A$ and $V_{\mathrm{ERG}}$ approach the ideal values with $O(h^2)$ error.

3) Smooth$_{\varepsilon}$ (when and how)

Goal: stabilize normals and reflections without exceeding $\varepsilon$.

  1. Local Taubin/MLS filter (forward/backward pass to avoid shrinkage).
  2. Projection onto the sphere ($\lVert v\rVert \to R$).
  3. Check: Hausdorff (pre/post) $\le \varepsilon/2$.
  4. Smoothed normals from local MLS fit ($\ge C^{1}$ continuity).

When it’s not needed: if you only measure area/ERG volume and faceting is already below the $\varepsilon$-scale threshold.

4) Algorithm (concise)

input: R, ε
κ ← 1/R
h_max ← 2*sqrt(ε/κ)       # = 2*sqrt(εR)
N    ← round((2π/√3) * R/ε)

P ← fibonacci_sphere(N)    # or icosphere(h_max)
T ← triangulate_on_sphere(P)
orient(T)                  # outward normals

A ← sum_areas(T)
V_ERG ← tetra_volume(T)

if need_smooth_normals:
    P' ← taubin_mls(P, T)  # controlled smoothing
    P' ← project_to_sphere(P', R)
    assert hausdorff(P, P') ≤ ε/2
    recompute_normals(P', T)
output: (P, T, A, V_ERG, normals)

5) Checks & validation

  • Hausdorff distance (ideal ↔ mesh) $\le \varepsilon$.
  • Triangle quality (avoid extreme angles).
  • No self-intersections.
  • $O(h^{2})$ convergence for area and ERG volume.

6) Why it matters

The sphere is an ideal testbed: constant curvature and closed-form $A,V$. The chain points → surface → ERG volume → smooth at scale $\varepsilon$ sets the general GRG/ERG procedure for solids.

7) Figures (inline SVG)

Sagitta geometry: s ≈ h^2/(8R) Arc of radius R, chord of length h, sagitta s; all lengths in the same units. R O s | ⟂ h
F3 — Sagitta relation used to bound $h_{\max}$.
Quasi-uniform points on a sphere Wireframe sphere with dots to suggest Fibonacci vs icosphere distributions.
F1 — Point distribution (Fibonacci vs icosphere idea) at equal $h$.

8) FAQ

Is “perfect” absolute?
No: it is perfect at scale $\varepsilon$. Details $<\,\varepsilon$ are not guaranteed.

Do we always need smoothing?
No: needed for normals/optics stability; otherwise optional.

Fibonacci or icosphere?
Both work: Fibonacci is simple and isotropic; icosphere offers regular connectivity.

How do I choose $\varepsilon$?
Based on use: measurement accuracy, rendering, fabrication, etc.

ERG Quick Calculator ERG grid icon Concentric arcs with dyadic ticks representing ERG refinement.

This compact tool computes the quarter-sampling step Δu and the grid size K from the dyadic level b, previews the uk values, and exports the grid to CSV.

Inputs

  • Dyadic level b ∈ ℕ≥0 (recommended range: 0–18)
  • Optional: recent estimates V2b-1 and V2b to check the dyadic stopping rule
\[ \Delta u \;=\; 2^{-(b+2)}, \qquad K \;=\; \left\lfloor \frac{1}{\Delta u} \right\rfloor \;=\; 2^{\,b+2}. \]
\[ \text{Stop if}\quad \bigl|V_{2^{b}} - V_{2^{b-1}}\bigr| \le \varepsilon. \]

Calculator

Results

  • Δu = — (exact: —)
  • K = — (i.e., number of grid points)
  • N = — (turns-first level, N = 2b)
Preview of u-grid uk = k · Δu

First 8: —

Last 8: —

—

Practical checklist

  • Use dyadic refinement: increase b until the dyadic difference falls below ε.
  • Quarter-sampling is assumed: Δu = 2-(b+2).
  • Grid is deterministic; CSV can be versioned for reproducibility.
ERG – Radial (Turns)

ERG – Radial (Turns)

ERG — Radial (Turns)

Method block (turns-based). Angles are measured in turns (fractions of a full rotation, u∈[0,1)). We write c(u), s(u) for period-1 cosine/sine in turns (so c(0)=1, s(0)=0; c(1/4)=0, s(1/4)=1). No sexagesimal units and no external constants appear in the primary formulas.

Radial node

For a circle of radius r and an angle u (turns):

$$ P(u) \;=\; \bigl(r\,c(u),\; r\,s(u)\bigr), \qquad u\in[0,1). $$

Uniform partition over the full turn: $u_k = k/N$, step $\Delta u = 1/N$.

Fig. A — Radial node with turns arc Axes, a circle, two radii separated by an angle u in turns, an arc marking u, and the point P(u). u P(u) O
Fig. A — Radial point $P(u)=(r\,c(u),\,r\,s(u))$ with angle $u$ expressed in turns.

Circumference (equal-angle chords)

Each chord between $P(u_k)$ and $P(u_{k+1})$ has length $2r\,s(\Delta u/2)$. Sum of $N$ identical chords → product:

$$ \boxed{\,C_N \;=\; 2\,N\,r\,s\!\Bigl(\tfrac{1}{2N}\Bigr)\,} $$

Interpretation: inscribed regular $N$-gon; $C_N$ increases with $N$ and converges to the circle’s circumference.

Fig. B — Regular N-gon from equal-angle chords (N=12) Circle of radius 100 with twelve equal-angle chords forming an inscribed regular polygon. N = 12, Δu = 1/N
Fig. B — Equal-angle chords tile the full turn (regular $N$-gon).

Area (equal-angle sectors)

The $N$ isosceles sectors (sides $r,r$ and angle $\Delta u$) each have area $\tfrac12 r^2 s(\Delta u)$. Sum → product:

$$ \boxed{\,A_N \;=\; \tfrac{N}{2}\,r^2\,s\!\Bigl(\tfrac{1}{N}\Bigr)\,} $$

$A_N$ increases with $N$ and converges to the circle’s area.

Fig. C — Sectors at equal angular step Two illustrative sectors on a circle, approximately 1/8 turn each, showing area by equal-angle sectors. Δu = 1/N (turns)
Fig. C — Area by sectors at equal angular step (sum of identical pieces).

How to use

  • Pick a precision N (e.g., 128–1024). If you store angles as fixed-point turns k/2^B, choose N dividing 2^B.
  • Step-doubling check: compare results at N vs 2N to gauge the remaining gap.

Pseudocode (2D)

Input: r, N
C = 2 * N * r * s( 1 / (2*N) )
A = 0.5 * N * r^2 * s( 1 / N )
  

Notes

  • Turns keep formulas simple and hardware-friendly (fixed-point angle indices, LUTs, SIMD).
  • Use this block when you want a pure angular build; for Cartesian builds see Δx Trapezoidal and Original Projection pages.

Angle unit & precision (turns, binary fixed-point)

We measure angles in turns: a full rotation is 1 turn. Hence quarter-turn = 1/4, half-turn = 1/2, etc. Trigonometric functions are period-1 in turns: c(u), s(u) with c(0)=1, s(0)=0, c(1/4)=0, s(1/4)=1.

Equal-angle partition

Choose an integer N (number of sectors) and set the angular step Δu = 1/N. The sampling angles are uk = k/N, k=0,…,N−1.

Binary fixed-point turns (B bits)

For hardware/software precision, store angles as u = k / 2^B turns with k ∈ {0,…,2^B−1}. The angular resolution is ΔuB = 1 / 2^B. If you want exactly N equal sectors, pick N that divides 2^B (e.g., N = 2^B), and use indices k = m·j with m = 2^B / N, j = 0,…,N−1.

Why more bits ⇒ more accuracy

  • Circumference (chords): CN = 2 N r · s(1/(2N)) is the perimeter of the inscribed regular N-gon and increases to the circle’s circumference. With N=2^B, the step halves when B→B+1 and the error typically drops ~×4 (quadratic in the step).
  • Area (sectors): AN = ½ N r² · s(1/N) is the area of N equal sectors and increases to the circle’s area; same step-squared behaviour.
0 1/8 1/4 3/8 1/2 5/8 3/4 7/8
Example with B = 3 bits ⇒ 23 = 8 ticks. Increasing B doubles the ticks and the precision.

Pseudocode (B-bit angles)

Input: r, B
N = 1 << B            // N = 2^B sectors
C = 2 * N * r * s( 1.0 / (2 * N) )
A = 0.5 * N * r^2 * s( 1.0 / N )

Implementation tip: if you keep an angle register k modulo 2^B, additions are wrap-around on B bits. For LUTs of size 2^M with M ≤ B, you can index by k >> (B−M).

GRG Original Projection

GRG Original Projection

Earlier Formulation

This page preserves a historical GRG method. Its notation and formulas belong to that version. The current binary radial formulation and verification are available here. Historical computational claims require separate validation.

Original Projection — historical method This page presents the original GRG idea: the circle is generated from the inside. The circle area is computed on a quadrant by projecting heights onto the x-axis and using midpoint rectangles (discrete upper); a matching right-endpoint rule gives a discrete lower, forming an under/over corridor that shrinks as $N$ increases (the midpoint rule is second-order). The perimeter is obtained from the sum of equal-angle chords on the quadrant (then $\times 4$). This method remains alongside other GRG blocks and is kept intact for comparison and continued study. See also Core Turns and Δx Trapezoidal.

Original Projection (Quarter → ×4)

Work on the quarter $x\in[0,r]$ with the profile $y(x)=\sqrt{r^{2}-x^{2}}$. Use uniform $\Delta x=r/N$. Midpoint rectangles provide a discrete upper estimate; right-endpoint rectangles provide a discrete lower. Multiply by $4$ to obtain full-circle values.

Setup

$$ \Delta x \;=\; \frac{r}{N}, \qquad x_k \;=\; k\,\Delta x \ (k=0,\dots,N), \qquad x_{k+\tfrac12} \;=\; \Bigl(k+\tfrac12\Bigr)\Delta x, \qquad y(x) \;=\; \sqrt{\,r^{2}-x^{2}\,}. $$

Quarter area: discrete corridor (upper vs lower)

Midpoint (discrete upper, second-order)

$$ A_{\text{quarter}}^{\text{mid}}(N) \;=\; \sum_{k=0}^{N-1} \Delta x \; y\!\bigl(x_{k+\tfrac12}\bigr), \qquad A_{\text{circle}}^{\text{mid}}(N) \;=\; 4\,A_{\text{quarter}}^{\text{mid}}(N). $$

Right-endpoint (discrete lower)

$$ A_{\text{quarter}}^{\text{right}}(N) \;=\; \sum_{k=0}^{N-1} \Delta x \; y\!\bigl(x_{k+1}\bigr), \qquad A_{\text{circle}}^{\text{right}}(N) \;=\; 4\,A_{\text{quarter}}^{\text{right}}(N). $$

Corridor: $A_{\text{circle}}^{\text{right}}(N) \;\le\; \text{Area(circle)} \;\le\; A_{\text{circle}}^{\text{mid}}(N)$, with gap shrinking like $O(N^{-2})$ under smoothness.

Perimeter via equal-angle chords (quadrant → ×4)

Partition the quarter by equal angular steps in turns. Let the quarter have $Q$ equal-angle chords of step $\Delta u=\tfrac{1}{4Q}$. The sum over the quarter is

$$ C_{\text{quarter}}(Q) \;=\; 2\,Q\,r\,s\!\Bigl(\tfrac{\Delta u}{2}\Bigr) \;=\; 2\,Q\,r\,s\!\Bigl(\tfrac{1}{8Q}\Bigr), \qquad C_{\text{circle}} \;\approx\; 4\,C_{\text{quarter}}(Q) \;=\; 8\,Q\,r\,s\!\Bigl(\tfrac{1}{8Q}\Bigr). $$

Equivalently, with $N=4Q$ steps on the full turn: $C_{N}=2\,N\,r\,s\!\bigl(\tfrac{1}{2N}\bigr)$ (see Core Turns).

Figure — Quarter with midpoint and right rectangles

Quarter: midpoint (upper) vs right-endpoint (lower) Quarter arc of a circle (r=100) with Δx strips. Green: midpoint rectangles; orange: right-endpoint rectangles. Both lie inside the quarter; midpoint sits above right. x y midpoint (upper) right (lower)
Midpoint vs right-endpoint corridor on the quarter.

Why use this block

  • Explicit under/over corridor with midpoint/right rules on the quarter.
  • Second-order convergence for the midpoint rule ($O(N^{-2})$) with simple operations.
  • No angle handling; complements chord-based perimeter via equal-angle steps.

How to use

  • Choose $N$ (e.g., $200$–$1000$) for the quarter; multiply results by $4$ for the circle.
  • Step-doubling check: compare $N$ vs $2N$ to estimate the residual gap between upper and lower.
  • Pair with equal-angle chords on the quarter to report both area and perimeter consistently.

See also

Core Turns · Δx Trapezoidal · Applications / Circle

Original Projection

The original GRG area method: sample the quarter along the x-axis with uniform step $\Delta x=r/N$. At each sample, project the height on the circle graph $y(x)=\sqrt{r^{2}-x^{2}}$ and build discrete rectangles. Two rules create a shrinking corridor: midpoint rectangles (upper) and right-endpoint rectangles (lower). Multiply by $4$ for the full circle. No angles are required in this block.

Setup

$$ \Delta x \;=\; \frac{r}{N}, \qquad x_k \;=\; k\,\Delta x \quad (k=0,\dots,N), \qquad x_{k+\tfrac12} \;=\; \Bigl(k+\tfrac12\Bigr)\Delta x, \qquad y(x) \;=\; \sqrt{\,r^{2}-x^{2}\,}. $$

Quarter-area sums (→ ×4 for the circle)

$$ \textbf{Midpoint (upper):}\quad A_{\mathrm{mid}}^{\mathrm{q}}(N) \;=\; \sum_{k=0}^{N-1} y\!\bigl(x_{k+\tfrac12}\bigr)\,\Delta x $$
$$ \textbf{Right-end (lower):}\quad A_{\mathrm{right}}^{\mathrm{q}}(N) \;=\; \sum_{k=0}^{N-1} y\!\bigl(x_{k+1}\bigr)\,\Delta x $$
$$ \textbf{Circle totals:}\quad A_{\mathrm{mid}} \;=\; 4\,A_{\mathrm{mid}}^{\mathrm{q}}, \qquad A_{\mathrm{right}} \;=\; 4\,A_{\mathrm{right}}^{\mathrm{q}} $$
$$ \textbf{Corridor:}\quad A_{\mathrm{right}} \;\le\; A_{\mathrm{true}} \;\le\; A_{\mathrm{mid}} $$
$$ \textbf{Estimate (optional):}\quad A_{\mathrm{avg}} \;=\; \frac{A_{\mathrm{mid}}+A_{\mathrm{right}}}{2} \quad\text{(use half-gap as an error bar).} $$

Notes

  • $y(x)=\sqrt{r^{2}-x^{2}}$ is concave on $[0,r]$; hence midpoint gives an upper estimate and right-endpoint a lower one.
  • Increase $N$ to tighten the corridor; publish $A_{\mathrm{avg}}$ with its half-gap if you need an error bar.

See also: Δx Trapezoidal · Core Turns · Applications / Circle

Chemistry

Chemistry

Generative Radial Geometry for Chemistry: From Conformers to MOFs and Solvent Shells

Angles in turns. We sample directions with turns \(u\in[0,1)\) at \(\Delta u=1/N\) (full turn). This keeps angular steps digital-native and π-free.
g(r)

Generative Radial Geometry (GRG) offers a center-out way to construct and search chemical structures. By organizing atoms, coordination sites, pores, or solvent molecules in radial shells with controlled distances and angles, GRG cuts down the combinatorial explosion and makes 3D models that are physically plausible and immediately ready for simulation.

Where GRG helps in chemistry

  • Molecule modeling & design: targeted conformer generation around rings and chiral centers; pre-screening of virtual libraries to propose sterically sensible radial scaffolds.
  • Crystallography & solids: crystal packing via radial neighborhoods of a repeat unit; localized models of defects and vacancies.
  • Molecular dynamics: fast computation of radial distribution functions (RDF) and balanced initialization of solvents/ions around a solute.
  • Porous materials (MOF/COF): radial placement of metal nodes around linkers; geometric control of free radii to tune pore accessibility.
  • Supramolecular self-assembly: prediction of micelles/liposomes and core–shell architectures by concentric, composition-aware layers.
  • Drug design & docking: radial abstractions of binding pockets and “radial grids” of electrostatic potential to guide polar/apolar moieties.
GRG Modes & Selection (Chemistry). We use three base modes: Δx Trapezoidal (area-like sums on a quarter, lower estimate), Projection Corridor (paired lower/upper bounds on a quarter), and Chord-Sum at Δu (loops on the full turn, lower; pair with tangent-sum for an upper bound). In 3D they extend naturally to spherical shells/belts/frusta.

Δx Trapezoidal (Cartesian)

Target: fast area/volume roll-ups • Estimate: lower • Domain: quarter (×4)

  • RDF histograms (shell counts), coordination numbers (baseline).
  • Solvent occupancy per shell; pore cross-section scans.

Projection Corridor

Target: certified bounds on integrals • Estimate: lower & upper • Domain: quarter (×4)

  • Bounds for \(N(R)=4\pi\rho\!\int_0^R\!g(r)\,r^2dr\) and shell occupancies.
  • Stop when gap ≤ tolerance; use to compare force fields robustly.

Chord-Sum at Δu (Radial)

Target: ring/loop sampling & perimeter • Estimate: lower (add tangent-sum ↑) • Domain: full turn

  • Uniform directions \(u\in[0,1)\) for conformers/solvent placement.
  • Pore apertures & ring tiling in MOFs/COFs; angular RDF slices.

Picker by task. Need speed → Trapezoid; need guarantees/threshold radii → Corridor; need angular uniformity/phase on rings → Chord-Sum (± tangent-sum); volumetrics → shell/belt extensions.

Core GRG idea for chemical systems

Place partners within radial bounds and enforce angular/steric constraints; then score candidates and iterate. Typical constraints:

$$ r_{\min} \;\le\; r \;\le\; r_{\max}, \qquad \angle(\text{A–C–B}) \;\ge\; \alpha_{\min}. $$

For distributions, the classic RDF (pair correlation) reads:

$$ g(r) \;=\; \frac{1}{4\pi r^{2}\,\rho\,N}\, \sum_{i\ne j}\, \delta\!\bigl(r-\lVert \mathbf{r}_i-\mathbf{r}_j \rVert \bigr). $$

GRG modes: Use Trapezoid to accumulate RDF shell counts quickly; switch to Corridor for certified bounds on coordination \(N(R)=4\pi\rho\!\int_0^R\!g(r)\,r^2dr\); use Chord-Sum at \(\Delta u=1/N\) to ensure uniform angular sampling when RDF is evaluated over directional sectors.

Worked examples

1) Conformer generation around a chiral center

Goal: explore the spatial arrangements around a chiral carbon and select the most stable isomer.

  1. Define the chiral center C and the four substituents (A, B, C, D).
  2. Choose distance bounds for C–X: e.g., 1.45–1.55 Å.
  3. Partition the interval into k concentric shells (e.g., 5).
  4. On each shell, sample directions with turns \(u\in[0,1)\) at \(\Delta u=1/N\), enforcing tetrahedral angles ≈\(109.5^\circ\) and min separations.
  5. Score with a light force field (e.g., UFF) and retain the lowest-energy 10 conformers.
C* A B C D Constraints: 1.45 ≤ r(C–X) ≤ 1.55 Å ∠ ≈ 109.5° (tetrahedral) Shells: 5

GRG modes: Chord-Sum (full turn, turns \(u\)) for uniform angular sampling and ring-wise sterics; Trapezoid to tally shell feasibility quickly; Corridor to certify bounds on steric/energy scores over shells before QM refinement.

2) Crystal packing of a simple MOF

Goal: arrange metal nodes and organic linkers in a cubic unit cell using radial symmetry.

  1. Place a metal node M (e.g., Zn2+) at the cell center; four linkers L at the corners of a radial tetrahedron.
  2. Set coordination bounds (e.g., M–O = 1.9–2.2 Å).
  3. For each L site, sample positions on a spherical shell about M, keeping \(\angle\text{L–M–L}\approx 109.5^\circ\).
  4. Tile the cell periodically with vectors \((a,0,0)\), \((0,a,0)\), \((0,0,a)\).
  5. Run a short geometry minimization (e.g., Powell) to relieve strain.
M L L L L

GRG modes: Chord-Sum for ring apertures and angular registry of linkers (periodic tiling over full turn); Trapezoid for cross-sectional pore area scans (quarter ×4); Corridor to bound pore-limiting/free-sphere radii derived from those scans.

3) Solvent bubble for MD around a solute

Goal: generate a balanced water sphere around a charged solute without overcrowding.

  1. Locate the solute center of mass and choose \(R_1\) (solute + first shell) and \(R_2\) (outer boundary).
  2. Split \([R_1,R_2]\) into \(N\) shells (typically 3–5).
  3. For each shell, place water molecules by sampling directions uniformly with turns \(u\) and \(\Delta u=1/N\); set distances \(r\) within that shell and enforce \(d_{\min}(\mathrm{O}, \text{solute}) \ge 2.5\ \text{Å}\).
  4. Assign water orientations (H–O–H) with small random perturbations.
  5. Export to PDB and run a short heating/minimization to relax the sphere.
solute

GRG modes: Chord-Sum for uniform angular placement/orientations; Trapezoid for quick shell occupancy and radial density; Corridor to bracket hydration numbers \(N(R)\) and to stop when bounds meet your tolerance.

4) Docking on radial electrostatic grids (quick setup)

Goal: approximate binding pocket neighborhoods with radial shells and guide pose sampling.

  1. Center a pocket reference and define shells \([r_k,r_{k+1}]\) plus ring samples at turns \(u_j=j/N\).
  2. Precompute coarse electrostatic potential on these cells; score ligand fragments by shell and ring.
  3. Promote top cells to fine sampling; enforce sterics and ring-wise clashes; export poses to your docking engine.

GRG modes: Chord-Sum for ring coverage of orientations; Trapezoid to roll up cell scores radially; Corridor to keep upper/lower envelopes on pocket accessibility/energy as you refine.

From generation to computation

  • Search space reduction: symmetries and radial bounds focus the exploration on chemically sensible regions.
  • 3D realism with control: enforce minimum/maximum inter-center distances and angles while sampling.
  • Drop-in to pipelines: GRG output meshes with QM, MD, and docking workflows (e.g., UFF pre-screen → PDB export → MD heating → production run).

GRG modes (pipeline): Use Trapezoid during fast scans; switch to Corridor to certify thresholds (coordination/hydration/pore radii); validate angular uniformity/perimeters with Chord-Sum (± tangent-sum) before committing to costly runs.

Conclusion

Across molecular design, crystal engineering, porous frameworks, self-assembly, and simulation setup, GRG brings a clear center-out logic: define radial bounds, discretize into shells, generate angles under constraints, and score. Choosing among Δx Trapezoidal, Projection Corridor, and Chord-Sum at Δu—or combining them—yields fast baselines, certified bounds, and robust angular control for meaningful chemistry.

RDF & Coordination via GRG Corridor — bounds on N(R) and Rn

Definitions. With bulk number density \(\rho\) and radial distribution \(g(r)\), the coordination number inside radius \(R\) is

$$ N(R)=4\pi\rho\int_0^{R} g(r)\,r^2\,dr. $$

Discrete GRG shells. Choose radii \(0=r_0turns \(u\in[0,1)\)) and use min/max over the sector.

Corridor bounds (cumulative up to \(R\)).

$$ N^{\downarrow}(R)=\rho\!\!\sum_{k:\,r_{k+1}\le R}\! V_k\,g_k^{\min},\qquad N^{\uparrow}(R)=\rho\!\!\sum_{k:\,r_{k+1}\le R}\! V_k\,g_k^{\max}, $$
where \(g_k^{\min},g_k^{\max}\in\{g_k^{\mathrm{in}},g_k^{\mathrm{out}}\}\) for smooth/monotone segments, or the angular min/max in that shell otherwise. Always \(N^{\downarrow}(R)\le N(R)\le N^{\uparrow}(R)\).

Bracketing a coordination radius. For a target coordination \(n\) (e.g., “first shell”):

  1. \(R_{n}^{-}=\min\{R:\,N^{\uparrow}(R)\ge n\}\) is a lower bound of the true \(R_n\).
  2. \(R_{n}^{+}=\min\{R:\,N^{\downarrow}(R)\ge n\}\) is an upper bound of the true \(R_n\).
  3. Refine by halving shell width \(\Delta r\) near the bracket or by bisecting within the shell until \(R_{n}^{+}-R_{n}^{-}\le\) tolerance.

Method picker. Isotropic liquids: use shells only (fast). Structured/anisotropic systems or near interfaces: split shells into polar cells; sample azimuth with Chord-Sum (\(\Delta u=1/N\)) to keep directional coverage, then apply the corridor per cell. Use Trapezoid for quick scans of \(N(R)\); switch to Corridor when you need guarantees.

N_up above true N, N_down below, horizontal n line; bracket on R. R N n R− R+

Practical notes. Use \(\Delta r\) small enough to resolve the first peak of \(g(r)\) (typ. 0.02–0.05 nm); respect PBC and the minimum-image convention (limit \(R\le L/2\) in a cubic box). For noisy \(g(r)\), smooth lightly after computing corridor bounds, not before.

Optics

Optics

Generative Radial Geometry for Optics: From Aspheres to Metasurfaces

Generative Radial Geometry (GRG) treats optical elements as radially generated structures optimized from the center outward. This viewpoint enables targeted aberration correction, compact/lightweight systems, and fast iteration via simulation—spanning refractive aspheres, GRIN profiles, diffractive zone plates, and radially programmed metasurfaces.

What GRG means in optics

In GRG, a surface or refractive-index profile is parameterized radially and then optimized against a merit function (e.g., wavefront error, Strehl, or MTF) over the full pupil. Rather than restricting to a low-order conic/asphere, GRG explores richer radial degrees of freedom that better align the phase over wide apertures and fields.

GRG Modes & Selection for Optics. We use three base modes: Δx Trapezoidal (fast area-like radial sums, lower estimate), Projection Corridor (paired lower/upper area bounds via right/midpoint sampling), and Chord-Sum at Δu (circumference/loops on the full turn, lower; pair with tangent-sum for an upper bound). In optics they map to pupil integrals (energy/WFE), certified bounds on merit terms, and phase/loop controls on rings/zones.

Δx Trapezoidal (Cartesian)

Target: area-weighted radial sums (pupil cross-sections) • Estimate: lower

  • Encircled energy, WFE/OPD RMS, throughput vs radius.
  • Baseline fast integration in design loops.

Projection Corridor

Target: same as above • Estimate: lower & upper (certified)

  • Bounds for energy, WFE, Strehl/MTF contributions.
  • Use to stop/refine when gap ≤ tolerance.

Chord-Sum at Δu (Radial)

Target: loops on rings (full turn) • Estimate: lower (pair with tangent-sum ↑)

  • Zone edges, phase wraps (2π), vortex/Bessel rings.
  • Perimeter/phase uniformity & ring tiling quality.

Picker by task. Quick merit updates → Trapezoid; need guarantees → Corridor; ring/zone phase & perimeter → Chord-Sum (± tangent-sum); 3D volume/weight/thermal → shell/frusta extensions.

Why GRG improves optical design

  • Targeted aberration correction: spherical aberration, coma, and astigmatism can be minimized across large apertures by flattening phase error over the beam.
  • Compact, lightweight systems: high-performance single elements can replace multi-lens groups; GRG also supports radial GRIN to combine focus and correction in one body.
  • Advanced diffractive elements: optimized radial zone partitioning for resolution, efficiency, and robustness—supporting multi-order/multi-focal designs.
  • Metasurfaces & LIDAR: radial placement/shaping of nano-scatterers for phase/amplitude control (beam shaping, Bessel/vortex), wide-FOV collimation, compact 360° sensing.
  • Rapid simulation-to-prototype: GRG loops tightly with FEM/FDTD engines to explore candidate radial profiles quickly.

Design workflow (radial parametrization → merit function → solver)

A typical GRG workflow parameterizes the sag or index as a radial series; samples the pupil; defines a merit function over wavefront or image metrics; and solves for the radial coefficients (often via linearization around a base conic).

Radial surface model

We model the sag z(r) as a base conic plus a radial polynomial tail:

$$ z(r) \;=\; \frac{c\,r^{2}}{\,1+\sqrt{\,1-(1+k)c^{2}r^{2}\,}\,} \;+\; a_{4}r^{4} \;+\; a_{6}r^{6} \;+\; a_{8}r^{8}. $$
Axis r vs z(r); blue curve shows base conic; accent curve shows GRG-corrected sag. r z base conic GRG tail

Sampling and merit function

Sample radii across the clear aperture and minimize wavefront residual at wavelength λ for the target focal length:

$$ \min_{a_4,a_6,a_8}\;\sum_{i} \bigl[\Phi\bigl(z(r_i)\bigr)\bigr]^2, $$
Circle aperture with 5 concentric rings and sample points.

Linearized solve

Linearizing in the coefficients leads to a system

$$ M \begin{pmatrix} a_{4}\\[2pt] a_{6}\\[2pt] a_{8} \end{pmatrix} \;=\; b. $$

GRG modes: Use Trapezoid for fast radial contributions to WFE/energy; switch to Corridor when you need a guaranteed bound on residuals; use Chord-Sum on rings to enforce phase consistency (2π wraps) and to check zone/perimeter uniformity; add tangent-sum to bracket loop metrics.

Worked example: aspheric–radial singlet at λ = 550 nm

For a collimated beam at λ=550 nm focused to f=100 mm with D=25 mm, take a base paraboloid (k=–1) with curvature c=0.010 mm⁻¹ (R=100 mm). Solving the linearized system yields:

$$ \begin{aligned} a_{4} &= 2.50\times 10^{-11}\,\mathrm{mm}^{-3},\\ a_{6} &= -1.20\times 10^{-16}\,\mathrm{mm}^{-5},\\ a_{8} &= 3.00\times 10^{-22}\,\mathrm{mm}^{-7}. \end{aligned} $$

With these coefficients, the residual wavefront error across the pupil falls below λ/20 and the MTF at 50 lp/mm improves by ~30% relative to the spherical counterpart:

$$ \begin{aligned} \mathrm{WFE}_{\mathrm{rms}} &\le \frac{\lambda}{20},\\ \mathrm{MTF}\!\left(50\,\mathrm{lp/mm}\right) &\approx 1.30\,\times\,\mathrm{MTF}_{\text{spherical}}. \end{aligned} $$
MTF curves vs spatial frequency; GRG shows higher contrast near 50 lp/mm. spatial freq (lp/mm) MTF 50 ~30% gain @ 50 lp/mm (GRG) spherical GRG Two small fan plots suggesting reduced aberrations after correction. Ray fan (tangential) Ray fan (sagittal)

GRG modes: Trapezoid for quick MTF/Strehl-related radial sums; Corridor to certify WFE/energy targets before freezing coefficients; Chord-Sum (+ tangent-sum) to monitor ring-wise phase/perimeter and edge artifacts.

Diffractive optics and zone plates

GRG optimizes the radial subdivision and phase steps of diffractive optical elements (DOEs) to jointly maximize resolution, first-order efficiency, and fabrication tolerance, and can be extended to multi-order/multi-focal targets.

Concentric rings with varying widths representing an optimized radial phase profile.

GRG modes: Chord-Sum to place ring edges by phase advance along the circumference (2π steps, vortex charge checking); Corridor to bound first-order efficiency/EE across radii; Trapezoid for throughput and fill-factor roll-ups.

Metasurfaces and 360° sensing (LIDAR)

For metasurfaces, GRG prescribes the radial distribution and geometry of nano-scatterers (meta-atoms) to deliver the desired phase/amp profile—enabling beam shaping (Bessel, vortex), wide-FOV collimation, or compact 360° sensing modules.

Dots arranged in concentric rings with varying densities and azimuthal offsets.

GRG modes: Chord-Sum for ringwise phase conformity and azimuthal uniformity (Bessel/vortex); Corridor to bracket efficiency across pupil zones under scatterer quantization; Trapezoid for fast aggregate metrics during layout sweeps.

GRIN materials and fabrication

Beyond pure surface shaping, GRG covers radial gradient-index (GRIN) profiles co-optimized with geometry, compatible with precision 3D printing, advanced lithography, and layered deposition processes.

Circle with radial gradient indicating higher index in the center. n(r)

GRG modes: Trapezoid/Corridor for OPD and energy integrals through shells (robustness to dispersion/tolerances); Chord-Sum to verify iso-phase circles after co-optimizing n(r) + sag.

Simulation loop and time-to-prototype

A GRG toolchain linked to wave/EM solvers rapidly screens candidate radial profiles, reducing the number of physical iterations needed before fabrication.

Blocks: Parametrization → Solver → EM Simulation → Tolerance → Prototype. Radial parametrization Solver EM simulation Tolerance Prototype

GRG modes: Loop fast with Trapezoid; certify with Corridor (stop when the bound gap is within tolerance); validate ring/zone behavior with Chord-Sum (+ tangent-sum) before tape-out.

Practical notes: tolerances, costs, and when GRG is worth it

  • Tolerancing: include manufacturing/assembly error budgets in the merit function so the solved profile remains robust after polishing, litho rounding, or index dispersion.
  • Cost trade-offs: in commodity systems, classic low-order aspheres may stay cheaper; GRG shines when performance/weight constraints justify advanced profiles.
  • System impact: a single GRG element can replace a small lens group—simplifying alignment and improving thermal stability—especially with GRIN or metasurface layers.

Conclusion

GRG augments—not replaces—classical optical design. By combining Δx Trapezoidal, Projection Corridor, and Chord-Sum at Δu (with tangent-sum for upper loop bounds), you get fast merit updates, certified guarantees, and precise ring/zone control across refractive, diffractive, GRIN, and metasurface optics.

Encircled Energy (EE) via GRG Corridor — bounds on Rτ

Definition. For a pupil-normalized PSF intensity \(I\), the encircled energy at radius \(R\) is

$$ E(R)=\frac{\iint_{x^2+y^2\le R^2}\! I(x,y)\,dA}{\iint_{x^2+y^2\le R_{\max}^2}\! I(x,y)\,dA}\,. $$

Axisymmetric shortcut. If \(I(x,y)=I(r)\) then

$$ E(R)=\frac{2\pi\int_0^{R} r\,I(r)\,dr}{2\pi\int_0^{R_{\max}} r\,I(r)\,dr}\,. $$

GRG corridor (discrete). Choose radii \(0=r_0

Lower/upper cumulative EE (up to the smallest index with \(r_{k+1}\le R\)):

$$ E^{\downarrow}(R)=\frac{\sum_{k\,:\,r_{k+1}\le R} A_k\,I_{k}^{\min}}{\sum_{k=0}^{K-1} A_k\,I_{k}^{\mathrm{mid}}},\qquad E^{\uparrow}(R)=\frac{\sum_{k\,:\,r_{k+1}\le R} A_k\,I_{k}^{\max}}{\sum_{k=0}^{K-1} A_k\,I_{k}^{\mathrm{mid}}}, $$
where \(I_k^{\min}, I_k^{\max}\) can be chosen as \(\{I_k^{\mathrm{out}}, I_k^{\mathrm{in}}\}\) for monotone-decreasing \(I(r)\), or via angular min/max for general PSFs. Always \(E^{\downarrow}(R)\le E(R)\le E^{\uparrow}(R)\).

Bracketing the EE radius. For a target \(\tau\) (e.g., 0.80):

  1. \(R_{\tau}^{-}=\min\{R:\,E^{\uparrow}(R)\ge \tau\}\) is a lower bound on the true \(R_{\tau}\).
  2. \(R_{\tau}^{+}=\min\{R:\,E^{\downarrow}(R)\ge \tau\}\) is an upper bound on the true \(R_{\tau}\).
  3. Refine by increasing annuli (or bisect within the bracket). Stop when \(R_{\tau}^{+}-R_{\tau}^{-}\le\) tolerance.

Method picker. Axisymmetric/on-axis: use annular corridor above (fast). General PSF or field points: use GRG Projection Corridor on a quarter (area bounds), or polar cells with per-cell min/max. Use Chord-Sum (+ tangent-sum) to validate ring perimeter/phase uniformity when EE is tied to zone edges.

E_up above true E, E_down below, horizontal tau line; bracket on R. R E τ Rτ− Rτ+