I am doing a PhD in economics so I work with quantities and I forgot to tell you that x>=0 and y>=0 all the time. Sorry for this missing information and thanks for your answer
As a matter of fact theta>0 too
Hello,
I need to find a two-arguments function u(x,y) which satisfies six constraints on its derivatives. x and y are quantities so always positive.
1&2: On the first derivatives:
du/dx>0 for all x & du/dy>0 for all y (so u is increasing in x and y)
3&4: On the second derivatives...