Hi,

I have a formula for a 3d vector field u(x,y,z) given by

{-((I Tanh[y C[2] + z C[3] - (x Sqrt[1 - 2 C[2]^2 - 2 C[3]^2])/Sqrt[2] + C[4]])/Sqrt[2]), 
-((Sqrt[3 - 2 C[7]^2] Tanh[y C[2] + z C[3] - (x Sqrt[1 - 2 C[2]^2 - 2 C[3]^2])/Sqrt[2] + C[4]])/Sqrt[2]), 
 C[7] Tanh[y C[2] + z C[3] - (x Sqrt[1 - 2 C[2]^2 - 2 C[3]^2])/Sqrt[2] + C[4]]}

and I want to find the set of constants (C[2], C[3], C[4], C[7]) which will minimize the squared difference between this function and a given target function of the form

{x,y,z}/Sqrt[x^2+y^2+z^2]*Tanh[Sqrt[x^2+y^2+z^2]/2]

Only real solutions are of interest to me. Can someone help me out on how to do this kind of thing in Mathematica ?