retningsafledede

Den retningsafledede af en funktion f(x,y) langs vektoren v er

d_vf = ∇f • v .

Undertiden benyttes definitionen

d_vf = ∇f • v/|v|

 Den retningsafledede
                                          D_uf = ∇ f · u = | ∇ f | · cos(θ)

                                                   ∂f        ∂f        ∂f
                                          ∇ f = ---- i + ---- j + ---- k
                                                  ∂x        ∂y       ∂z    

                                        
                                         

todimensionelt
 

 Den retningsafledede
                                          D_uf = ∇ f · u = | ∇ f | · cos(θ)

                                                   ∂f        ∂f       
                                          ∇ f = ---- i + ---- j
                                                  ∂x        ∂y