savecase fails when solving OPF of IEEE RTS from command line

[rwl]

As reported by Prabakaran on the mailing list:

I recently installed PYPOWER in my Ubuntu 14.04, Python 2.7.6, scipy 0.13.3 and ran the sample commands given in GitHub project page's readme. When running the command,

$ opf -c case24_ieee_rts --solvedcase=rtsout.py

to solve an OPF for the IEEE Reliability Test System and write the solved case to file.

[mfripp]

If you're getting the message TypeError: %d format: a number is required, not numpy.ndarray, this seems to be a bug in savecase.py. You can fix it by changing line 143 of savecase.py (the file location should be referenced in the traceback that is printed when the error occurs). Near the end of line 143, change
bus[:, :MU_VMIN + 1]
to
bus[i, :MU_VMIN + 1]
(i.e., change the first colon to an i).