derivative of a function of two variables

Hello,

How can I get such a derivative in Matlab-Symbolic Toolbox ?

Differentiation according to two variables q1 and q2.

y=L1*cos(q1)+L2*cos(q2)
y´=-L1*sin(q1)-L2*cos(q2)

There is only this alternative?

z´=diff(y,q1)+diff(y,q2)

Thank you very much

[onur karakurt]

Thanks, but this is symbolic derivative, Can you give example numerical derivative with the function of y=L1*cos(q1)+L2*cos(q2)

Answer 1

[Kaijie Cui]

To get a numerical difference (symmetric difference), you calculate (f(x+dx)-f(x-dx))/(2*dx)

or "gradient", "polyder" (calculates the derivative of a polynomial) functions. Also a function "derivest" could also give numerical differentiation.

Answer 2

[Babak]

 y = L1*cos(q1)+L2*cos(q2)
 yp =-L1*sin(q1)-L2*cos(q2)

Do you want to take the derivative with respect to both independent parameters? if so, do this:

 dy_over_dq1_dq2 = diff(diff(y,q1),q2)

[Rasto]

But if derivatives under him dy_over_dq1_dq2 = diff(diff(y,q1),q2) in Matlab me comes 0.