Differentiation Of A Function.

Hi

I have a symbolic function,

S=sqrt(8).*(3.*X.^3+3.*Y.^2.*X-2.*X);

I need to differentiate it w.r.t X and Y. I did this by-

Tx=diff(S,X);
Ty=diff(S,Y);

I simply got the expression of the differentiation but I need to find the value of the differentiation w.r.t X and Y where X and Y varies from -1 to +1 in steps of 128 (i.e.X=-1:2/127:+1; Y=-1:2/127:+1;[X ,Y]=meshgrid(-1:2/127:+1,-1:2/127:+1);). So, can anyone please help me in finding out the value of the differentiation at all those mentioned points?

Thanking You!

Answer 1

[Andrei Bobrov]

syms X Y real
S=sqrt(8).*(3.*X.^3+3.*Y.^2.*X-2.*X);
F = jacobian(S,[X,Y]);
Fun = arrayfun(@(i1)matlabFunction(F(i1)),1:2,'un',0);

solution

[x,y] = meshgrid(linspace(-1,1,128));
p = cellfun(@(z)z(x,y),Fun,'un',0);
[dSdx,dSdy] =p{:};

[Pranjal Pathak]

Thanks a lot!It really did solve my problem.

Answer 2

[Andrew Newell]

You could do the following (I tack num onto the name to indicate it is numerical, not symbolic):

Xnum = linspace(-1,1,128); Ynum = Xnum;
[Xnum,Ynum] = meshgrid(Xnum,Ynum);
Txnum = double(subs(Tx,[X,Y],{Xnum,Ynum}));
Tynum = double(subs(Ty,[X,Y],{Xnum,Ynum}));