Problem using subs function

Question

KOZI 2018-10-23

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/425722-problem-using-subs-function

编辑： YT 2018-10-23

I am trying to plot Electric vectors of magnetic field.I have f function and then i am trying as the example to use gradient and quiver.My code is:

syms x y;
M=(4*abs(x))/((abs(x) + 1)^2 + y^2);
L=ellipticK(M);
f=(2*L/(pi*((abs(x) + 1)^2 + y^2)^(1/2)));
g = gradient(f, [x, y]);
[X, Y] = meshgrid(-1:.1:1,-1:.1:1);
G1 = subs(g(1), [x y], {X,Y});
G2 = subs(g(2), [x y], {X,Y});
quiver(X, Y, G1, G2)

And i get this error:

Error using symengine
Division by zero.
Error in sym/subs>mupadsubs (line 150)
G = mupadmex('symobj::fullsubs',F.s,X2,Y2);
Error in sym/subs (line 135)
    G = mupadsubs(F,X,Y);
Error in E (line 7)
G1 = subs(g(1), [x y], {X,Y});

Any help will be very useful. I am realy noob in matlab. I only need a plot for a homework. thanks in advance.

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Answer 1

YT 2018-10-23

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/425722-problem-using-subs-function#answer_343040

编辑：YT 2018-10-23

在 MATLAB Online 中打开

Even without being an expert in Matlab, the error should be pretty clear.

Division by zero.

This makes sense because X and Y both contain zeros, look at the meshgrid input

[X, Y] = meshgrid(-1:.1:1,-1:.1:1);
% -1:.1:1 => -1 -.9 -.8 -.7 -.6 -.5 -.4 -.3 -.2 -.1 0 .1 .2 .3 .4 .5 .6 .7 .8 .9 1

So I would remove the zeros from X and Y for it to work

syms x y;
M=(4*abs(x))/((abs(x) + 1)^2 + y^2);
L=ellipticK(M);
f=(2*L/(pi*((abs(x) + 1)^2 + y^2)^(1/2)));
g = gradient(f, [x, y]);
[X, Y] = meshgrid(-1:.1:1,-1:.1:1);
X(X==0)=[]; %removes zeros from X
Y(Y==0)=[]; %removes zeros from Y
G1 = subs(g(1), [x y], {X,Y});
G2 = subs(g(2), [x y], {X,Y});
quiver(X, Y, G1, G2)