fatal error in opf_setup with case33bw on older Matlab

[rdzman]

Thanks to to Jane Cheung for reporting this on Nov 21, 2018 on the MATPOWER-L mailing list (direct link not currently available to due to issues with the MATPOWER-L archive).

Running runopf('case33bw') results in the following fatal error in Matlab versions prior to R2016b (9.1).

>> runopf('case33bw')
Error using +
Matrix dimensions must agree.

Error in opf_setup (line 212)
    cpg(ip1) = cpg(ip1) + pcost(ip1, COST) * baseMVA;

Error in opf (line 225)
om = opf_setup(mpc, mpopt);

Error in runopf (line 75)
[r, success] = opf(casedata, mpopt);

This appears to be a caused by a bug in Matlab where it throws an error when adding empty matrices if any of the dimensions do not match.