Plot several parameter cases in one run

Replace the single A/B/C constants and --x0 option with a CASES table;
each case writes <name>.png and <name>.pdf. Add the A = diag(2, 0.75),
x0 = (0, -0.6) case.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

plot_mu_trajectories.py

@@ -19,9 +19,11 @@ from matplotlib.lines import Line2D
 
 from quadric import TOL, Ellipsoid
 
-A = np.array([[2.0, 0.0], [0.0, 1.0]])
-B = np.zeros(2)
-C = -1.0
+# One figure per case, for the ellipse x'Ax + b'x + c = 0 (b = 0 and c = -1 by default).
+CASES = {
+    'x_trajectories_mu_1': dict(A=np.diag([2.0, 1.0]), x0=[0.0, -0.1]),
+    'x_trajectories_mu_2': dict(A=np.diag([2.0, 0.75]), x0=[0.0, -0.6]),
+}
 
 N_PER_BRANCH = 266    # mu samples between consecutive poles
 EPS = 0.01            # gap left on each side of a pole
@@ -163,16 +165,23 @@ def use_latex_fonts():
 def main():
     use_latex_fonts()
     parser = argparse.ArgumentParser(description=__doc__.splitlines()[0])
-    parser.add_argument('--x0', type=float, nargs=2, default=[0.0, -0.1], metavar=('X1', 'X2'))
-    parser.add_argument('--output', type=Path, default=Path('figures/x_trajectories_mu'),
-                        help='output path, without extension (a .png and a .pdf are written)')
+    parser.add_argument('cases', nargs='*', metavar='CASE',
+                        help=f'cases to plot, among {", ".join(CASES)} (default: all)')
+    parser.add_argument('--output-dir', type=Path, default=Path('figures'))
     parser.add_argument('--show', action='store_true')
     args = parser.parse_args()
+    unknown = set(args.cases) - set(CASES)
+    if unknown:
+        parser.error(f'unknown cases: {", ".join(sorted(unknown))}')
 
-    fig = plot_trajectories(Ellipsoid(A, B, C), np.array(args.x0))
-    args.output.parent.mkdir(parents=True, exist_ok=True)
-    for extension in ('.png', '.pdf'):
-        fig.savefig(args.output.with_name(args.output.name + extension))
+    args.output_dir.mkdir(parents=True, exist_ok=True)
+    for name in args.cases or CASES:
+        case = CASES[name]
+        Q = Ellipsoid(case['A'], case.get('b', np.zeros(2)), case.get('c', -1.0))
+        fig = plot_trajectories(Q, np.array(case['x0']))
+        for extension in ('.png', '.pdf'):
+            fig.savefig(args.output_dir / (name + extension))
+        print('wrote', args.output_dir / name)
     if args.show:
         plt.show()