It is described a mathematical solving circuit (100) comprising: a crosspoint matrix (M.sub.G) including a plurality of row conductors (L.sub.i), a plurality of column conductors (C.sub.j) and a plurality of analog resistive memories (Gij), each connected between a row conductor and a column conductor; a plurality of operational amplifiers (OA.sub.i) each having: a first input terminal (IN.sub.1i) connected to a respective row conductor (L.sub.i), a second input terminal (IN.sub.2i) connected to a ground terminal (GR) at least one operational amplifier (OA.sub.i) of the plurality being such to take the respective first input terminal (IN.sub.1i) to a virtual ground.

It is described a mathematical solving circuit (100) comprising: a crosspoint matrix (M.sub.G) including a plurality of row conductors (L.sub.i), a plurality of column conductors (C.sub.j) and a plurality of analog resistive memories (Gij), each connected between a row conductor and a column conductor; a plurality of operational amplifiers (OA.sub.i) each having: a first input terminal (IN.sub.1i) connected to a respective row conductor (L.sub.i), a second input terminal (IN.sub.2i) connected to a ground terminal (GR) at least one operational amplifier (OA.sub.i) of the plurality being such to take the respective first input terminal (IN.sub.1i) to a virtual ground.

A method may include determining a decision space representing a set of content items to be presented on a user interface of a social networking site, the decision space accounting for competing quadratic constraints and interaction effects, estimating the decision space to linearize the competing quadratic constraints, determining, in the estimated decision space and using an objective function, a display probability for each content item in the set of content items, each respective display probability corresponding to a given content item's probability of display in a specific content slot of a plurality of content slots on the user interface; and causing display of the content items with the highest display probabilities.