Quadratic Optimization

But that is a single equality quadratic constraint, and I believe 
'quadratic constraints' (note, plural) conventionally means multiple 
inequality constraints.  That meaning is a hard problem that needs 
specialized software (most likely using interior-point methods).

   SpG>       Maximize a'x subject to x'Ax=c.

Not I believe the usual meaning (nor what Googling 'quadratic 
constraints' came up with for me).