Using simplify and first level signatures not as expected

[lingyiyang]

For a toy stream defined with integer increments (of 1), I would expect that a simplified stream to match its first level signature, or perhaps due to mismatch, a point may be removed. However, there are some unexpected results with rather strange first level terms.

CTX = rp.get_context(width=2, depth=4, coeffs=rp.DPReal)
word_stream = rp.LieIncrementStream.from_increments(np.array([[1., 0.],[0., 1.],  [1., 0.], [0., 1.], [1., 0.]]),
                                                    resolution=4, ctx=CTX)
partition = rp.Partition(rp.RealInterval(0.,5.0), intermediates=[0., 0.7, 1.2, 1.7, 2.3, 3.1, 5.0])
simple_stream = word_stream.simplify(partition, resolution=4, ctx=CTX, depth=2)
print(word_stream.log_signature(depth=3))
print(simple_stream.log_signature(depth=3))

which returns

{ 3(1) 2(2) -0.5([1,[1,2]]) -0.5([2,[1,2]]) }
{ 5.15789(1) 2(2) -2.15789([1,2]) -0.802862([1,[1,2]]) -1.2193([2,[1,2]]) }