WIP: Update lm_space distance_array method

- Remove mmax. Now, lmax == mmax
- Create index and l-number on the fly

nifty/spaces/lm_space/lm_helper.pyx

 import numpy as np
 cimport numpy as np
 
-cpdef _distance_array_helper(np.int_t x, np.ndarray[np.int_t] l,
-                             np.int_t original_size, np.int_t lmax):
+cpdef _distance_array_helper(np.ndarray[np.int_t] index_array, np.int_t lmax):
     cdef np.int size = (lmax + 1) * (lmax  + 1)
 
-    cdef np.ndarray res = np.zeros([size], dtype=np.float128)
-    res[0:lmax + 1] = np.arange(lmax + 1)
+    cdef np.ndarray res = np.zeros([len(index_array)], dtype=np.float128)
 
-    for i in xrange(original_size - lmax - 1):
-        res[i * 2 + lmax + 1] = l[i + lmax + 1]
-        res[i * 2 + lmax + 1] = l[i + lmax + 1]
+    for idx, index_full in enumerate(index_array):
+        if index_full <= lmax:
+            index_half = index_full
+        else:
+            index_half = (index_full + lmax + 1) / 2;
+        m = (np.ceil(((2 * lmax + 1) -
+                      np.sqrt((2 * lmax + 1)**2 -
+                              8 * (index_half - lmax))) / 2)).astype(int)
+        res[idx] = index_half - m * (2 * lmax + 1 - m) // 2
 
-    return res[x]
+    return res

nifty/spaces/lm_space/lm_space.py

@@ -75,7 +75,7 @@ class LMSpace(Space):
             Pixel volume of the :py:class:`lm_space`, which is always 1.
     """
 
-    def __init__(self, lmax, mmax=None, dtype=np.dtype('complex128')):
+    def __init__(self, lmax, dtype=np.dtype('complex128')):
         """
             Sets the attributes for an lm_space class instance.
 
@@ -111,7 +111,6 @@ class LMSpace(Space):
 
         super(LMSpace, self).__init__(dtype)
         self._lmax = self._parse_lmax(lmax)
-        self._mmax = self._parse_mmax(mmax)
 
     def distance_array(self, distribution_strategy):
         dists = arange(
@@ -122,7 +121,7 @@ class LMSpace(Space):
         l = hp.Alm.getlm(lmax=self.lmax)[0]
         dists = dists.apply_scalar_function(
             lambda x: _distance_array_helper(
-                int(x), l, hp.Alm.getsize(self.lmax), self.lmax
+                x, self.lmax
                 )
             )
 
@@ -177,7 +176,7 @@ class LMSpace(Space):
 
     @property
     def mmax(self):
-        return self._mmax
+        return self._lmax
 
     def _parse_lmax(self, lmax):
         lmax = np.int(lmax)
@@ -189,20 +188,3 @@ class LMSpace(Space):
             about.warnings.cprint(
                 "WARNING: unrecommended parameter (lmax <> 2*n+1).")
         return lmax
-
-    def _parse_mmax(self, mmax):
-        if mmax is None:
-            mmax = self.lmax
-        else:
-            mmax = int(mmax)
-
-        if mmax < 1:
-            raise ValueError(about._errors.cstring(
-                "ERROR: mmax < 1 is not allowed."))
-        if mmax > self.lmax:
-            raise ValueError(about._errors.cstring(
-                "ERROR: mmax > lmax is not allowed."))
-        if mmax != self.lmax:
-            about.warnings.cprint(
-                "WARNING: unrecommended parameter combination (mmax <> lmax).")
-        return mmax