Histogram manipulations and fitting -> zfit example

[JacekHoleczek]

In the "Histogram manipulations and fitting" chapter, in the "Fitting histograms" section, the last example uses "zfit".

I needed to "install zfit" from conda-forge, which generated a warning that 3 packages needed to be downgraded:

  - typing_extensions             4.7.1  pyha770c72_0             conda-forge     Cached
  + typing_extensions             4.5.0  pyha770c72_0             conda-forge       31kB
  - typing-extensions             4.7.1  hd8ed1ab_0               conda-forge     Cached
  + typing-extensions             4.5.0  hd8ed1ab_0               conda-forge       10kB
  - platformdirs                 3.10.0  pyhd8ed1ab_0             conda-forge     Cached
  + platformdirs                  3.5.1  pyhd8ed1ab_0             conda-forge       19kB

[jpivarski]

Currently, zfit is based on TensorFlow, which has restrictive installation dependencies. We're all looking forward to it being rewritten to use JAX instead, which is still a heavy dependency, but forward-looking.

(TensorFlow's future doesn't look good.)

[stale]

This issue or pull request has been automatically marked as stale because it has not had recent activity. Please manually close it, if it is no longer relevant, or ask for help or support to help getting it unstuck. Let me bring this to the attention of @klieret @wdconinc @michmx for now.