Issue with star.py --optimize=Cheb

[kevinkhu]

I have been adapting Starfish for use on low resolution DeVeny and Hydra spectra with input BT-Settl models containing temperature and log g information. When I get to the optimize Cheb step I encounter the following error which I can't trace to its origin:

$ star.py --optimize=Cheb
/home/kevin/.conda/envs/starfish/lib/python3.6/site-packages/numpy/polynomial/polyutils.py:334: RuntimeWarning: invalid value encountered in double_scalars
  off = (old[1]*new[0] - old[0]*new[1])/oldlen
/home/kevin/.conda/envs/starfish/lib/python3.6/site-packages/numpy/polynomial/polyutils.py:335: RuntimeWarning: divide by zero encountered in true_divide
  scl = newlen/oldlen
/home/kevin/.conda/envs/starfish/lib/python3.6/site-packages/numpy/polynomial/_polybase.py:292: RuntimeWarning: invalid value encountered in multiply
  arg = off + scl*arg
grid pars are [ 2800.      4.5]
Process Process-1:
Traceback (most recent call last):
  File "/home/kevin/.conda/envs/starfish/lib/python3.6/multiprocessing/process.py", line 258, in _bootstrap
    self.run()
  File "/home/kevin/.conda/envs/starfish/lib/python3.6/multiprocessing/process.py", line 93, in run
    self._target(*self._args, **self._kwargs)
  File "/home/kevin/Fishy/Starfish/Starfish/parallel.py", line 555, in brain
    alive = self.interpret()
  File "/home/kevin/Fishy/Starfish/Starfish/parallel.py", line 573, in interpret
    response = func(arg)
  File "/home/kevin/Fishy/Starfish/Starfish/parallel.py", line 482, in optimize_Cheb
    result = fmin(fprob, p0, maxiter=10000, maxfun=10000)
  File "/home/kevin/.conda/envs/starfish/lib/python3.6/site-packages/scipy/optimize/optimize.py", line 408, in fmin
    res = _minimize_neldermead(func, x0, args, callback=callback, **opts)
  File "/home/kevin/.conda/envs/starfish/lib/python3.6/site-packages/scipy/optimize/optimize.py", line 532, in _minimize_neldermead
    fsim[k] = func(sim[k])
  File "/home/kevin/.conda/envs/starfish/lib/python3.6/site-packages/scipy/optimize/optimize.py", line 292, in function_wrapper
    return function(*(wrapper_args + args))
  File "/home/kevin/Fishy/Starfish/Starfish/parallel.py", line 474, in fprob
    lnp = self.evaluate()
  File "/home/kevin/Fishy/Starfish/Starfish/parallel.py", line 293, in evaluate
    factor, flag = cho_factor(CC)
  File "/home/kevin/.conda/envs/starfish/lib/python3.6/site-packages/scipy/linalg/decomp_cholesky.py", line 142, in cho_factor
    check_finite=check_finite)
  File "/home/kevin/.conda/envs/starfish/lib/python3.6/site-packages/scipy/linalg/decomp_cholesky.py", line 19, in _cholesky
    a1 = asarray_chkfinite(a) if check_finite else asarray(a)
  File "/home/kevin/.conda/envs/starfish/lib/python3.6/site-packages/numpy/lib/function_base.py", line 1215, in asarray_chkfinite
    "array must not contain infs or NaNs")
ValueError: array must not contain infs or NaNs

I'm wondering if this is related to #21, but I don't have any infs or NaNs in my input flux or sigma arrays.