Question: PDE with unusual boundary conditions.

Hi. Solving a problem of non-linear oscilations of thin string I met a PDE with unusual bcs at the right side of the string: 
((diff(xi(x, t), t))^2-a1-b1*x)*(1+(diff(phi(x), x))*(diff(xi(x, t), x)))+c1*(diff(xi(x, t), x))*(diff(xi(x, t), t))*(2*(diff(phi(x), x))-(diff(xi(x, t), x)))*sqrt(1+(diff(xi(x, t), x))^2) = 0 , where phi is known function. Can I somehow use built-in  numeric solving pde methods with one of conditions provided as a descrete equation of descrete values of a unknown function. 

Please Wait...