' - - File: V_Vec1.txt

' Find the directional derivative of F{x,y} = x^2 * y  + x * y^2 in the direction of a unit vector
'      of angle pi/3 radians.  Then its numerical value, Dr(2,3).

F{x,y} = x^2 * y  + x * y^2
Fx{x} = Diff[F,x]                           ' Partial with respect to x.
Fy{y} = Diff[F,y]                           ' Partial with respect to y.
Fz{z} = 0
pi = 3.14159

U<t> = <Cos[pi/3], Sin[pi/3], 0>   ' Unit vector.
Fp<t> = <Fx, Fy, Fz>

Dr{t} = sDot[U,Fp] 

<x = 2 ; y = 3>                                ' Value at Dr{2,3}



