Discrepancies in Moment-Cuvature results

[DanielGMorenaFhecor]

When calculating the moment-curvature diagram, discrepancies were found compared to established software.

@MestreCarlos prepared examples, illustrations, and notes to track this issue in Point 11 explained this file

[talledodiego]

I think the issue may be the same as in #140 #141 #142.
Please take a look if this is the case. Otherwise we can go deeper into it.

Quick responses to Point 11:

Why only return the negative domain of curvature with theta=0? Wouldn't it be better to have the whole domain instead of use theta parameter for that?

See response to #142

The moment-curvature results should start at (0,0). I miss that point.

It is just a matter of choice include or not the point (0,0). It is not a problem to add a (0,0) when obtained results. With modification by @mortenengen for better defining the list of curvatures I think this can be done as well.

[mortenengen]

.calculate_moment_curvature() now accepts the keyword argument chi_first which can be set to 0.0 to include this value in the list of curvatures 😃

I am closing this issue, since it seems to cover the same topic as #140, #141 and #142, but it highlights the need for a careful description of the coordinate system in the docs.