From cabdcd2aefb64ea412cef70a2361e0027bf197c2 Mon Sep 17 00:00:00 2001
From: Gui-FernandesBR <guilherme_fernandes@usp.br>
Date: Thu, 18 Apr 2024 18:35:14 -0400
Subject: [PATCH] MNT: Refactor Flight class root finding algorithm for rail
 exit and impact time calculations

---
 rocketpy/simulation/flight.py | 34 ++++++++++++----------------------
 1 file changed, 12 insertions(+), 22 deletions(-)

diff --git a/rocketpy/simulation/flight.py b/rocketpy/simulation/flight.py
index 13aa40659..a3ab6fda3 100644
--- a/rocketpy/simulation/flight.py
+++ b/rocketpy/simulation/flight.py
@@ -818,18 +818,13 @@ def __simulate__(self, verbose):
                         b = float((3 * y1 - yp1 * D - 2 * c * D - 3 * d) / (D**2))
                         a = float(-(2 * y1 - yp1 * D - c * D - 2 * d) / (D**3)) + 1e-5
                         # Find roots
-                        d0 = b**2 - 3 * a * c
-                        d1 = 2 * b**3 - 9 * a * b * c + 27 * d * a**2
-                        c1 = ((d1 + (d1**2 - 4 * d0**3) ** (0.5)) / 2) ** (1 / 3)
-                        t_roots = []
-                        for k in [0, 1, 2]:
-                            c2 = c1 * (-1 / 2 + 1j * (3**0.5) / 2) ** k
-                            t_roots.append(-(1 / (3 * a)) * (b + c2 + d0 / c2))
+                        t_roots = Function.cardanos_root_finding(a, b, c, d)
                         # Find correct root
-                        valid_t_root = []
-                        for t_root in t_roots:
-                            if 0 < t_root.real < t1 and abs(t_root.imag) < 0.001:
-                                valid_t_root.append(t_root.real)
+                        valid_t_root = [
+                            t_root.real
+                            for t_root in t_roots
+                            if 0 < t_root.real < t1 and abs(t_root.imag) < 0.001
+                        ]
                         if len(valid_t_root) > 1:
                             raise ValueError(
                                 "Multiple roots found when solving for rail exit time."
@@ -914,18 +909,13 @@ def __simulate__(self, verbose):
                         b = float((3 * y1 - yp1 * D - 2 * c * D - 3 * d) / (D**2))
                         a = float(-(2 * y1 - yp1 * D - c * D - 2 * d) / (D**3))
                         # Find roots
-                        d0 = b**2 - 3 * a * c
-                        d1 = 2 * b**3 - 9 * a * b * c + 27 * d * a**2
-                        c1 = ((d1 + (d1**2 - 4 * d0**3) ** (0.5)) / 2) ** (1 / 3)
-                        t_roots = []
-                        for k in [0, 1, 2]:
-                            c2 = c1 * (-1 / 2 + 1j * (3**0.5) / 2) ** k
-                            t_roots.append(-(1 / (3 * a)) * (b + c2 + d0 / c2))
+                        t_roots = Function.cardanos_root_finding(a, b, c, d)
                         # Find correct root
-                        valid_t_root = []
-                        for t_root in t_roots:
-                            if 0 < t_root.real < t1 and abs(t_root.imag) < 0.001:
-                                valid_t_root.append(t_root.real)
+                        valid_t_root = [
+                            t_root.real
+                            for t_root in t_roots
+                            if abs(t_root.imag) < 0.001 and 0 < t_root.real < t1
+                        ]
                         if len(valid_t_root) > 1:
                             raise ValueError(
                                 "Multiple roots found when solving for impact time."