syms x y
fx=diff('4*y*x^3+5*x*y^2+x*y+6',x)     % diff( )：求x偏導(dǎo)數(shù)
fy=diff('4*y*x^3+5*x*y^2+x*y+6',y)     % diff( )：求y偏導(dǎo)數(shù)
fx =
        12*y*x^2+5*y^2+y
        fy =
        4*x^3+10*x*y+x