Added uniform w helper method, better derivative

src/scgenerator/helpers.py

@@ -14,14 +14,18 @@ from scgenerator.parameter import Parameters
 from scgenerator.physics.fiber import beta2, n_eff_hasan, n_eff_marcatili
 from scgenerator.physics.materials import n_gas_2
 from scgenerator.physics.simulate import RK4IP
-from scgenerator.physics.units import c
+from scgenerator.physics.units import c, nm
 
 try:
     from tqdm import tqdm
 except ModuleNotFoundError:
     tqdm = None
 
-__all__ = ["capillary_dispersion", "capillary_zdw", "revolver_dispersion","quick_sim"]
+__all__ = ["capillary_dispersion", "capillary_zdw", "revolver_dispersion", "quick_sim", "w_from_wl"]
+
+
+def w_from_wl(wl_min_nm: float, wl_max_nm: float, n: int) -> np.ndarray:
+    return np.linspace(nm(wl_max_nm), nm(wl_min_nm), n)
 
 
 def capillary_dispersion(

src/scgenerator/math.py

@@ -619,12 +619,14 @@ def stencil_coefficients_set(n: int, order: int) -> tuple[np.ndarray, np.ndarray
 
 
 def differentiate_arr(
-    values: np.ndarray, diff_order: int, extent: int, correct_edges=True
+    values: np.ndarray,
+    diff_order: int,
+    extent: int | None = None,
+    h: float = 1.0,
+    correct_edges=True,
 ) -> np.ndarray:
     """
     takes a derivative of order `diff_order` using equally spaced values
-    **NOTE** : this function doesn't actually know about your grid spacing `h`, so you need to
-    divide the result by `h**diff_order` to get a correct result.
 
     Parameters
     ---------
@@ -632,10 +634,12 @@ def differentiate_arr(
         equally spaced values
     diff_order : int
         order of differentiation
-    extent : int
+    extent : int, optional
         how many points away from the center the scheme uses. This determines accuracy.
         example: extent=6 means that 13 (6 on either side + center) points are used to evaluate the
-        derivative at each point.
+        derivative at each point. by default diff_order + 2
+    h : float, optional
+        step size, by default 1.0
     correct_edges : bool, optional
         avoid artifacts by using forward/backward schemes on the edges, by default True
 
@@ -644,17 +648,20 @@ def differentiate_arr(
     https://en.wikipedia.org/wiki/Finite_difference_coefficient
 
     """
+    if extent is None:
+        extent = diff_order + 2
     n_points = (diff_order + extent) // 2
 
     if not correct_edges:
         central_coefs = central_stencil_coefficients(n_points, diff_order)
-        return np.convolve(values, central_coefs[::-1], mode="same")
-
+        result = np.convolve(values, central_coefs[::-1], mode="same")
+    else:
         left_coefs, central_coefs, right_coefs = stencil_coefficients_set(n_points, diff_order)
-    return np.concatenate(
+        result = np.concatenate(
             (
                 np.convolve(values[: 2 * n_points], left_coefs[::-1], mode="valid"),
                 np.convolve(values, central_coefs[::-1], mode="valid"),
                 np.convolve(values[-2 * n_points :], right_coefs[::-1], mode="valid"),
             )
         )
+    return result / h**diff_order

src/scgenerator/physics/fiber.py

@@ -926,6 +926,11 @@ def gap_from_capillaries(core_radius: float, tube_radius: float, n_tubes: int) -
     return 2 * (s * (tube_radius + core_radius) - tube_radius)
 
 
+def tube_radius_from_gap(core_radius: float, gap: float, n_tubes: int) -> float:
+    s = np.sin(np.pi / n_tubes)
+    return (core_radius * s - 0.5 * gap) / (1 - s)
+
+
 def normalized_frequency_vincetti(
     wl: np.ndarray, thickness: float, n_clad_2: np.ndarray, n_gas_2: np.ndarray
 ) -> np.ndarray:
@@ -1136,4 +1141,3 @@ def n_eff_vincetti(
 
     # eq. (21) in [1]
     return n_gas - 0.125 / n_gas * (u_nm(1, 1) * wl_for_disp / (np.pi * r_co_eff)) ** 2 + d_n_eff
-

src/scgenerator/physics/materials.py

@@ -6,6 +6,7 @@ from typing import TypeVar
 
 import numpy as np
 
+import scgenerator.math as math
 from scgenerator import utils
 from scgenerator.cache import np_cache
 from scgenerator.logger import get_logger
@@ -74,6 +75,28 @@ class Sellmeier:
     def n(self, wl: T, temperature: float | None = None, pressure: float | None = None) -> T:
         return np.sqrt(self.n_gas_2(wl, temperature, pressure))
 
+    def delta(self, wl: np.ndarray, wl_zero_disp: float) -> np.ndarray:
+        """
+        'delta' quantity that describes the gas dispersion according to eq. S7 in [1]
+
+        Parameters
+        ----------
+        wl : ndarray
+            wavelength in m
+        wl_zero_disp : float
+            zero dispersion wavelength in m
+
+        Reference
+        ---------
+        [1] TRAVERS, John C., GRIGOROVA, Teodora F., BRAHMS, Christian, et al. High-energy
+            pulse self-compression and ultraviolet generation through soliton dynamics in hollow
+            capillary fibres. Nature Photonics, 2019, vol. 13, no 8, p. 547-554.
+        """
+        factor = (math.u_nm(1, 1) / c) ** 2 * (0.5 * wl / np.pi) ** 3
+        f = np.gradient(np.gradient(self.chi(wl), wl), wl)
+        ind = math.argclosest(wl, wl_zero_disp)
+        return factor * (f / f[ind] - 1)
+
 
 class Gas:
     name: str