[Bugfix] model.compare(dataset) does not work for the RPI test script

[yoshikisd]

When running the transmission_RPI.py example script, an error is raised when calling model.compare(dataset); see failure log at the end. This bug seems to originate from the shape of sim_data in the following line

cdtools/src/cdtools/models/base.py

Line 875 in b3a70ec

sim_data = self.forward(*inputs).detach().cpu().numpy()[0]

Specifically, in the case of a FancyPtycho (and presumably other ptychography) model, the shape of sim_data will be (N, M). However, if an RPI model is used, the shape of sim_data becomes (N,), which causes an invalid shape error to get thrown when plotting an image.

The bugfix solves this issue by only adding the [0] whenever the shape of the sim_data is bigger than 2 dimensions.

Failure log

cdtools/src/cdtools/models/base.py:922: UserWarning: Attempting to set identical low and high xlims makes transformation singular; automatically expanding.
  self.slider = Slider(axslider, 'Pattern #', 0, len(dataset)-1, valstep=1, valfmt="%d")
Traceback (most recent call last):
  File "/homes/dayne/repositories/cdtools_yoshikisd/cdtools/examples/transmission_RPI.py", line 46, in <module>
    model.compare(dataset)
  File "/homes/dayne/repositories/cdtools_yoshikisd/cdtools/src/cdtools/models/base.py", line 940, in compare
    update(0)
  File "/homes/dayne/repositories/cdtools_yoshikisd/cdtools/src/cdtools/models/base.py", line 891, in update
    sim = axes[0].imshow(sim_data)
          ^^^^^^^^^^^^^^^^^^^^^^^^
  File "/homes/dayne/.conda/envs/cdtools_testing/lib/python3.12/site-packages/matplotlib/__init__.py", line 1473, in inner
    return func(
           ^^^^^
  File "/homes/dayne/.conda/envs/cdtools_testing/lib/python3.12/site-packages/matplotlib/axes/_axes.py", line 5895, in imshow
    im.set_data(X)
  File "/homes/dayne/.conda/envs/cdtools_testing/lib/python3.12/site-packages/matplotlib/image.py", line 729, in set_data
    self._A = self._normalize_image_array(A)
              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/homes/dayne/.conda/envs/cdtools_testing/lib/python3.12/site-packages/matplotlib/image.py", line 697, in _normalize_image_array
    raise TypeError(f"Invalid shape {A.shape} for image data")
TypeError: Invalid shape (1000,) for image data

[allevitan]

Thanks so much for fixing this - the change looks good to me.