test16 version as base for OOB gravity

verification/verify_rotating_frame_velocity.py

@@ -0,0 +1,32 @@
+#!/usr/bin/env python3
+"""Regression check for the test9/test10 fake-impulse bug."""
+import math
+
+
+def qx(deg):
+    a=math.radians(deg)/2
+    return (math.cos(a),math.sin(a),0.0,0.0)
+
+def conj(q):
+    w,x,y,z=q; return (w,-x,-y,-z)
+
+def mul(a,b):
+    aw,ax,ay,az=a; bw,bx,by,bz=b
+    return (aw*bw-ax*bx-ay*by-az*bz,
+            aw*bx+ax*bw+ay*bz-az*by,
+            aw*by-ax*bz+ay*bw+az*bx,
+            aw*bz+ax*by-ay*bx+az*bw)
+
+def rotate(q,v):
+    r=mul(mul(q,(0.0,*v)),conj(q)); return r[1:]
+
+def invrotate(q,v): return rotate(conj(q),v)
+def close(a,b,e=1e-9): return all(abs(x-y)<e for x,y in zip(a,b))
+
+local=(0.17,0.42,-0.08)
+for deg in (0,20,45,90,180):
+    world=rotate(qx(deg),local)
+    recovered=invrotate(qx(deg),world)
+    assert close(recovered,local)
+    print(f"X {deg:3d}: local={local} -> world={world} -> local={recovered}")
+print('OK: changing ship orientation changes world representation without changing local velocity')