move dhdl function from util module into gwinc module

free up the "util" namespace for other purposes not related to noise
calculation

gwinc/gwinc.py

 from __future__ import division
 import copy
 import numpy as np
-from numpy import log10, pi, sqrt
+from numpy import pi, sqrt, sin, exp, abs, log10
+import scipy.constants
 from collections import OrderedDict
 import logging
 
 from .precomp import precompIFO
 from . import suspension
-from . import util
 from . import noise
 from .plot import plot_noise
 
 
+def dhdl(f, armlen):
+    """Strain to length conversion for noise power spetra
+
+    This takes into account the GW wavelength and is only important
+    when this is comparable to the detector arm length.
+
+    From R. Schilling, CQG 14 (1997) 1513-1519, equation 5,
+    with n = 1, nu = 0.05, ignoring overall phase and cos(nu)^2.
+    A small value of nu is used instead of zero to avoid infinities.
+
+    Returns the square of the dh/dL function, and the same divided by
+    the arm length squared.
+
+    """
+    c = scipy.constants.c
+    nu_small = 0.05
+    omega_arm = pi * f * armlen / c
+    omega_arm_f = (1 - sin(nu_small)) * pi * f * armlen / c
+    omega_arm_b = (1 + sin(nu_small)) * pi * f * armlen / c
+    sinc_sqr = 4 / abs(sin(omega_arm_f) * exp(-1j * omega_arm) / omega_arm_f
+                       + sin(omega_arm_b) * exp(1j * omega_arm) / omega_arm_b)**2
+    # keep DC value equal to 1
+    sinc_sqr /= sinc_sqr[0]
+    dhdl_sqr = sinc_sqr / armlen**2
+    return dhdl_sqr, sinc_sqr
+
+
 def noise_calc(ifo, f):
     """Calculate all IFO noises and return as dict
 
@@ -46,7 +73,7 @@ def noise_calc(ifo, f):
     #
     # used for converting displacement to strain in all noise calculations
 
-    ifo.gwinc.dhdl_sqr, ifo.gwinc.sinc_sqr = util.dhdl(f, ifo.Infrastructure.Length)
+    ifo.gwinc.dhdl_sqr, ifo.gwinc.sinc_sqr = dhdl(f, ifo.Infrastructure.Length)
 
     ##############################
 

gwinc/util.py

-from numpy import pi, sin, exp, abs
-import scipy.constants
-
-
-def dhdl(f, armlen):
-    """Strain to length conversion for noise power spetra
-
-    This takes into account the GW wavelength and is only important
-    when this is comparable to the detector arm length.
-
-    From R. Schilling, CQG 14 (1997) 1513-1519, equation 5,
-    with n = 1, nu = 0.05, ignoring overall phase and cos(nu)^2.
-    A small value of nu is used instead of zero to avoid infinities.
-
-    Returns the square of the dh/dL function, and the same divided by
-    the arm length squared.
-
-    """
-    c = scipy.constants.c
-    nu_small = 0.05
-    omega_arm = pi * f * armlen / c
-    omega_arm_f = (1 - sin(nu_small)) * pi * f * armlen / c
-    omega_arm_b = (1 + sin(nu_small)) * pi * f * armlen / c
-    sinc_sqr = 4 / abs(sin(omega_arm_f) * exp(-1j * omega_arm) / omega_arm_f
-                       + sin(omega_arm_b) * exp(1j * omega_arm) / omega_arm_b)**2
-    # keep DC value equal to 1
-    sinc_sqr /= sinc_sqr[0]
-    dhdl_sqr = sinc_sqr / armlen**2
-    return dhdl_sqr, sinc_sqr