Minor stuff.

Former-commit-id: c0de35f6a52ce4cc4f34cf4b417364d92e8dac4d

qpms/ewaldsf.c

@@ -37,6 +37,8 @@ void IgnoreUnderflowsGSLErrorHandler (const char * reason,
 
 // DLMF 8.7.3 (latter expression) for complex second argument
 // BTW if a is large negative, it might take a while to evaluate.
+// This can't be used for non-positive integer a due to
+// Г(a) in the formula.
 int cx_gamma_inc_series_e(const double a, const complex double z, qpms_csf_result * result) {
   if (a <= 0 && a == (int) a) {
     result->val = NAN + NAN*I;
@@ -160,7 +162,7 @@ int cx_gamma_inc_CF_e(const double a, const complex double z, qpms_csf_result *r
 }
 
 
-// incomplete gamma for complex second argument
+/// Incomplete gamma function for complex second argument.
 int complex_gamma_inc_e(double a, complex double x, qpms_csf_result *result) {
   if (creal(x) >= 0 &&
       (0 == fabs(cimag(x)) || // x is real positive; just use the real fun
@@ -172,9 +174,14 @@ int complex_gamma_inc_e(double a, complex double x, qpms_csf_result *result) {
     return retval;
   } else if (creal(x) >= 0 && cabs(x) > 0.5)
     return cx_gamma_inc_CF_e(a, x, result);
-  else
+  else if (QPMS_LIKELY(a > 0 || (a % 1.0)))
     return cx_gamma_inc_series_e(a, x, result);
-  
+  else
+  /* FIXME cx_gamma_inc_series_e() probably fails for non-positive integer a.
+   * This does not matter for 2D lattices in 3D space, 
+   * but it might cause problems in the other cases.
+   */
+    QPMS_NOT_IMPLEMENTED("Incomplete Gamma function with non-positive integer a.");
 }
 
 // Exponential integral for complex argument; !UNTESTED! and probably not needed, as I expressed everything in terms of inc. gammas anyways.

qpms/qpms_c.pyx

@@ -592,6 +592,12 @@ def pitau(double theta, qpms_l_t lMax, double csphase = -1):
     qpms_pitau_fill(&leg[0], &pi[0], &tau[0], theta, lMax, csphase)
     return (lega, pia, taua)
 
+def linton_gamma(cdouble x):
+    return clilgamma(x)
+
+def linton_gamma_real(double x):
+    return lilgamma(x)
+
 def gamma_inc(double a, cdouble x):
     cdef qpms_csf_result res
     with pgsl_ignore_error(15): #15 is underflow

qpms/qpms_p.py

@@ -1,5 +1,5 @@
 import numpy as np
-from qpms_c import *
+from .qpms_c import *
 ň = np.newaxis
 import scipy
 from scipy.constants import epsilon_0 as ε_0, c, pi as π, e, hbar as ℏ, mu_0 as μ_0