Dipolarkernal speedup

[HKaras]

A significant speed up of the dipolar kernal

Currently the effective dipolar evolution time vector is interpolated on every run of dipolar kernal even though it never changes. Interpolation should be avoid as much as possible as it is very slow in Python. This interpolation is now cached so it only done once per pathway.

Speedup: (Using CVXOPT nnlssolver) 9.0s -> 7.9s 10% faster (Using quadprog nnlssolver) 2.8s -> 2.2s 20 % faster

CProfile (using quadprog): Before:

   471585 function calls (454090 primitive calls) in 2.776 seconds

   Ordered by: internal time
   List reduced from 765 to 10 due to restriction <10>

   ncalls  tottime  percall  cumtime  percall filename:lineno(function)
       60    0.584    0.010    0.585    0.010 linalg.py:1499(svd)
      101    0.549    0.005    0.550    0.005 linalg.py:492(inv)
      115    0.413    0.004    0.447    0.004 _bsplines.py:1138(make_interp_spline)
      101    0.207    0.002    0.929    0.009 selregparam.py:190(_evalalpha)
      157    0.153    0.001    0.164    0.001 solvers.py:1104(qpnnls)
      115    0.119    0.001    0.981    0.009 dipolarmodel.py:427(Vtwospin_nonlinear_fcn)
      157    0.095    0.001    0.096    0.001 solvers.py:88(_lsqcomponents)
      230    0.056    0.000    0.056    0.000 _bsplines.py:511(_evaluate)
       56    0.032    0.001    1.593    0.028 solvers.py:581(linear_problem)
      115    0.029    0.000    0.855    0.007 dipolarkernel.py:22(dipolarkernel)

After:

      450059 function calls (432453 primitive calls) in 2.194 seconds

   Ordered by: internal time
   List reduced from 766 to 10 due to restriction <10>

   ncalls  tottime  percall  cumtime  percall filename:lineno(function)
      101    0.704    0.007    0.705    0.007 linalg.py:492(inv)
       60    0.424    0.007    0.425    0.007 linalg.py:1499(svd)
      101    0.199    0.002    1.088    0.011 selregparam.py:190(_evalalpha)
      157    0.149    0.001    0.158    0.001 solvers.py:1104(qpnnls)
      157    0.108    0.001    0.108    0.001 solvers.py:88(_lsqcomponents)
      115    0.063    0.001    0.409    0.004 dipolarmodel.py:427(Vtwospin_nonlinear_fcn)
      230    0.035    0.000    0.035    0.000 _bsplines.py:511(_evaluate)
       56    0.029    0.001    1.613    0.029 solvers.py:581(linear_problem)
      115    0.026    0.000    0.339    0.003 dipolarkernel.py:22(dipolarkernel)
12876/348    0.024    0.000    0.078    0.000 arrayprint.py:789(recurser)