Change density to density_compensators

[Lenoush]

change : tfmri.estimate_density( samples, shape, method="pipe", max_iter=15)
to : tf.math.reciprocal_no_nan(tfmri.estimate_density( samples, shape, method="pipe", max_iter=15 ))

• need to add test

[paquiteau]

Don't worry too much about the density tests, density compensations methods will probably need a new tests setup in the future.

[chaithyagr]

This can be merged, @paquiteau ?

[paquiteau]

Maybe we should add the same normalization as you did for gpuNUFFT ?

[chaithyagr]

I was just going through the codes, we seem to have redundant similar pipe code at:

mri-nufft/src/mrinufft/operators/interfaces/tfnufft.py

Lines 139 to 157 in f49c8c0

	def pipe(samples, shape, n_iter=15):
	"""Estimate the density compensation using the pipe method.
	Parameters
	----------
	samples: Tensor
	The samples location of shape ``Nsamples x N_dimensions``.
	It should be C-contiguous.
	shape: tuple
	Shape of the image space.
	n_iter: int
	Number of iterations.
	Returns
	-------
	Tensor
	The estimated density compensation.
	"""
	return tfmri.estimate_density(samples, shape, method="pipe", max_iter=n_iter)

@Lenoush maybe can you do the same update there also and then make the call to the pipe class method? See what is done in gpuNUFFT to get clarity.

Also can you please also implement the normalization like it is done at :

https://github.com/chaithyagr/mri-nufft/blob/45bc400b2cfec8abee4c550780f7a6e5f1fa433c/src/mrinufft/operators/interfaces/gpunufft.py#L512-L517

[paquiteau]

Almost there ! This keeps getting better.

[chaithyagr]

One final thing left I guess: Change test_gpunufft.py to test_density,py and add a test to test the pipe method from tfnufft also.

[chaithyagr]

LGTM, We can merge this right @paquiteau ?