Cleanup of the python interface

[sandmaennchen]

• add print_stats() which prints a summary of the IP iterations
• add getter for lagrange multiplier to OCP QP solution
• consistent return type in getter of OCP QP solution: return a list whenever idx_end is given
• fix dimension of feedback gains
• cleanup python examples

[giaf]

It was correct at it was before, K is the state feedback matrix of size nu times nx.
It is probably a bit confusing, but n_row is the number of rows, not the length of each row.
Consistently with that, the (column) vectors lr, p and k have n_row but not n_col.

[giaf]

If you found numerically from the example that it was wrong as it was before, it may be that the issue is this: HPIPM writes back the result in column-major, but numpy matrices are row-major by default.
If this is the case, either the feedback matrix is saved in a temporary matrix and transposed into the actual one, or the zeros numpy matrix is set to column-major before getting the data from C, e.g. like in https://github.com/giaf/hpipm/blob/master/interfaces/python/hpipm_python/hpipm_python/wrapper/hpipm_ocp_qp.py#L75 (note that here we did for setters, but it may also make the job for the getters).

[sandmaennchen]

Column- vs. row-major was indeed the problem! thanks 👍

[giaf]

@sandmaennchen trying to compile the python interface, I get the error

    ERROR: Command errored out with exit status 1:
     command: /usr/bin/python3 -c 'import sys, setuptools, tokenize; sys.argv[0] = '"'"'/tmp/pip-req-build-4sianxjm/setup.py'"'"'; __file__='"'"'/tmp/pip-req-build-4sianxjm/setup.py'"'"';f=getattr(tokenize, '"'"'open'"'"', open)(__file__);code=f.read().replace('"'"'\r\n'"'"', '"'"'\n'"'"');f.close();exec(compile(code, __file__, '"'"'exec'"'"'))' egg_info --egg-base /tmp/pip-req-build-4sianxjm/pip-egg-info
         cwd: /tmp/pip-req-build-4sianxjm/
    Complete output (15 lines):
    Traceback (most recent call last):
      File "<string>", line 1, in <module>
      File "/tmp/pip-req-build-4sianxjm/setup.py", line 38, in <module>
        import hpipm_python
      File "/tmp/pip-req-build-4sianxjm/hpipm_python/__init__.py", line 36, in <module>
        from .common  import *
      File "/tmp/pip-req-build-4sianxjm/hpipm_python/common.py", line 37, in <module>
        from .wrapper.hpipm_solver import *
      File "/tmp/pip-req-build-4sianxjm/hpipm_python/wrapper/__init__.py", line 41, in <module>
        from .hpipm_ocp_qp_sol import *
      File "/tmp/pip-req-build-4sianxjm/hpipm_python/wrapper/hpipm_ocp_qp_sol.py", line 41, in <module>
        class hpipm_ocp_qp_sol:
      File "/tmp/pip-req-build-4sianxjm/hpipm_python/wrapper/hpipm_ocp_qp_sol.py", line 106, in hpipm_ocp_qp_sol
        def get(self, field: str, idx_start: int, idx_end: Optional[int] = None) -> Union[np.ndarray, list[np.ndarray]]:
    TypeError: 'type' object is not subscriptable
    ----------------------------------------
ERROR: Command errored out with exit status 1: python setup.py egg_info Check the logs for full command output.

I have python 3.8. It seems to be unhappy of the Union stuff, removing that the error is gone. Any hint?

[sandmaennchen]

Hi @giaf, type hints should now be backward compatible with python 3.8!
Will look into your other comments soon, sorry for the late reply 🙈