add_quad_cost

[Adjifack Nelson]

Good morning every bodyI am trying to add a cost function to opf flow model 
minimizing voltage difference. The added cost function is of the form 
sum(v(i)-1). I have tried to impletent it using add_quad_cost but i have 
errors. I have included an image of my matlab work space showing the error. 
With Q=[], c=-ones(33,1) and k=ones(33,1).Best regards