graph_sid for lower k

[jarlebring]

The methods:

• graph_sid
• graph_bbc
• graph_sastre

are currently not implemented for k<=3. The papers propose to use ps for this case since it is optimal. For completeness, I think we can add k<=3 also for these by making a call to graph_ps.

[jarlebring]

I think also graph_sastre_basic_exp should be changed to graph_sastre_exp.

[jarlebring]

and also basic in bbc can be removed

[eringh]

Should we also rename graph_sastre_basic(b) to, for example, graph_sastre_poly(b)?

[jarlebring]

Sounds good.