[markov chains] Use Consistent Math Notations

[HumphreyYang]

Hi @jstac,

This PR addresses our discussions in #105 about the consistent use of math notations.

I have put $\psi$ in the context of $t$ across the lecture since it is more consistent with the plots we have and our discussions in distributions over time.

Could you please review this PR and let me know if there is anything I should change?

Many thanks in advance.

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[jstac]

Please remove this change --- I think it's irrelevant when we just want to define a distribution.

(This is a judgement call on the trade-off between constency and simplicity.)

[jstac]

Many thanks @HumphreyYang , the lecture is clearer now. Just one small change above.

[HumphreyYang]

Many thanks for your review @jstac. I have reverted this change :)

[HumphreyYang]

Many thanks @jstac for the detailed read. I have updated the draft. One place I am not sure whether to use $\psi_0$ and $\psi_0$ is here. I think it we should leave it as it is now, but a quick confirmation would be greatly appreciated :)

[HumphreyYang]

Hi @mmcky, there seems to be a cache error similar to what we had before:

Exception occurred:
  File "/usr/share/miniconda3/envs/quantecon/lib/python3.9/site-packages/jupyter_cache/cache/db.py", line 57, in session_context
    raise RuntimeError(
RuntimeError: Unexpected error accessing jupyter cache, it may need to be cleared.
The full traceback has been saved in /tmp/sphinx-err-snkrx4oe.log, if you want to report the issue to the developers.
Please also report this if it was a user error, so that a better error message can be provided next time.
A bug report can be filed in the tracker at <https://github.com/sphinx-doc/sphinx/issues>. Thanks!
Traceback (most recent call last):
  File "/usr/share/miniconda3/envs/quantecon/lib/python3.9/site-packages/sqlalchemy/engine/base.py", line 1819, in _execute_context
    self.dialect.do_execute(
  File "/usr/share/miniconda3/envs/quantecon/lib/python3.9/site-packages/sqlalchemy/engine/default.py", line 732, in do_execute
    cursor.execute(statement, parameters)
sqlite3.OperationalError: no such table: nbproject

Could you please have a look to see if the cache needs to be cleaned?

Many thanks in advance.

[jstac]

Many thanks @jstac for the detailed read. I have updated the draft. One place I am not sure whether to use ψ0 and ψ0 is here. I think it we should leave it as it is now, but a quick confirmation would be greatly appreciated :)

I think that's fine as is @HumphreyYang . Many thanks.

@mmcky please merge when ready.