NumbaPerformanceWarning on KL

[paskino]

Description

Unit test shows a numba warning:

NumbaPerformanceWarning: 
prange or pndindex loop will not be executed in parallel due to there being 
more than one entry to or exit from the loop (e.g., an assertion).

File "cil/optimisation/functions/KullbackLeibler.py", line 346:
    def kl_div(x, y, eta):
        <source elided>
        accumulator = numpy.zeros(get_num_threads(), dtype=numpy.float64)
        for i in prange(x.size):
        ^

This is due to the else which returns, I believe.

CIL/Wrappers/Python/cil/optimisation/functions/KullbackLeibler.py

Lines 343 to 358 in bd21df3

	@njit(parallel=True)
	def kl_div(x, y, eta):
	accumulator = numpy.zeros(get_num_threads(), dtype=numpy.float64)
	for i in prange(x.size):
	X = x.flat[i]
	Y = y.flat[i] + eta.flat[i]
	if X > 0 and Y > 0:
	# out.flat[i] = X * numpy.log(X/Y) - X + Y
	accumulator[get_thread_id()] += X * numpy.log(X/Y) - X + Y
	elif X == 0 and Y >= 0:
	# out.flat[i] = Y
	accumulator[get_thread_id()] += Y
	else:
	# out.flat[i] = numpy.inf
	return numpy.inf
	return sum(accumulator)