With additional changes fixing some bugs and formatting. Especially the
commit messages.

fixed mistakes of equation expression in documentation and used abbrevation ip_data for _ip_data[ip] in line 206.

This crashed the convertGEO utility. Thanks to JM for reporting!
This bug was introduced with a6ff2c7a.

Fix PETSc norm computation

Compute b matrices on the fly

For easier reading.

This is slightly slower, but also uses less memory.

Fix secondary variable computation in HT process