Update changelog again and bump version to 2.11

jplephem/__init__.py

@@ -353,8 +353,10 @@ Changelog
 
 **2019 December 13 — Version 2.11**
 
-* Reverse the order in which the PCK Chebyshev polynomial is computed to
-  gain a partial digit of extra precision.
+* Reverse the order in which Chebyshev polynomials are computed to
+  slightly increase speed, to simplify the code, and in one case
+  (comparing PCK output to NASA) to gain a partial digit of extra
+  precision.
 
 **2019 December 11 — Version 2.10**
 

jplephem/pck.py

@@ -150,8 +150,7 @@ class Segment(object):
 
         coefficients = coefficients[:,:,index]
 
-        # Chebyshev polynomial.  We accumulate results starting with the
-        # final coefficient to retain accuracy for as long as possible.
+        # Chebyshev polynomial.
 
         s = 2.0 * offset / intlen - 1.0
         s2 = 2.0 * s
@@ -162,7 +161,7 @@ class Segment(object):
             w2 = w1
             w1 = w0
             w0 = coefficient + (s2 * w1 - w2)
-            if derivative:
+            if derivative:  # TODO: defer to a second loop
                 dw2 = dw1
                 dw1 = dw0
                 dw0 = 2.0 * w1 + dw1 * s2 - dw2

jplephem/spk.py

@@ -236,13 +236,12 @@ class Segment(BaseSegment):
 
         coefficients = coefficients[:,:,index]
 
-        # Chebyshev polynomial.  We accumulate results starting with the
-        # final coefficient to retain accuracy for as long as possible.
+        # Chebyshev polynomial.
 
         s = 2.0 * offset / intlen - 1.0
         s2 = 2.0 * s
 
-        w0 = w1 = dw0 = dw1 = 0.0
+        w0 = w1 = 0.0
         wlist = []
 
         for coefficient in coefficients[:-1]:
@@ -260,6 +259,8 @@ class Segment(BaseSegment):
 
         # Chebyshev differentiation.
 
+        dw0 = dw1 = 0.0
+
         for coefficient, w1 in zip(coefficients[:-1], wlist):
             dw2 = dw1
             dw1 = dw0

setup.py

@@ -8,7 +8,7 @@ import jplephem
 description, long_description = jplephem.__doc__.split('\n', 1)
 
 setup(name = 'jplephem',
-      version = '2.10',
+      version = '2.11',
       description = description,
       long_description = long_description,
       license = 'MIT',