problem with symbolic to function handle

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lorenzo donadio
lorenzo donadio 2016-11-1
评论： Walter Roberson 2016-11-1
Hi, i have a symbolic function of 3 variables and then I compute its gradient and convert each entry of the gradient to a function handle,but some of them become function handles of less than 3 variables, and that makes the evaluation of the vector field more difficult, any ideas on how to solve this?
syms x y z
f=x*y*z+x*2*y
G=gradient(f)
Dx=matlabFunction(G(1));
Dy=matlabFunction(G(2));
Dz=matlabFunction(G(3));
[X,Y,Z]=meshgrid(-3:1:3);
Fx=Dx(Y,Z);
Fy=Dy(X,Z);
Fz=Dz(X,Y);
this code works but i would like it to work when i write:
Fx=Dx( X,Y,Z);
Fy=Dy(X,Y,Z);
Fz=Dz(X,Y,Z);
and this is what my function handles look like:
Dx =
@(y, z) y .* z + 2 .* y
Dy =
@(x, z) x .* z + 2 .* x
Dz =
@(x, y) x .* y

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采纳的回答

Steven Lord
Steven Lord 2016-11-1
You can specify the list of input arguments the generated function or function handle should have using the 'Vars' parameter described in the documentation for the matlabFunction function. See the "Specify Input Arguments for Generated Function" example on that documentation page to see how to use this parameter.

更多回答（1 个）

Mischa Kim
Mischa Kim 2016-11-1
How about
syms x y z
f = x*y*z+x*2*y;
G = gradient(f);
m = matlabFunction(G);
[X,Y,Z] = meshgrid(-3:1:3);
m_eval = m(X,Y,Z);
  1 个评论
lorenzo donadio
lorenzo donadio 2016-11-1
this works but it doesnt solve the problem, because if i change the f function to lets say x^2+y^2+z now the gradient is only a function of x and y and doing
m = matlabFunction(G);
and then m_eval = m(X,Y,Z);
gives me and error,how can i fix it?

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