Plotting implicit equation with fimplicit

7 次查看（过去 30 天）
Jay
Jay 2019-2-11
评论： Torsten 2019-2-11
Hello
I have tried to plot this implicit equation. But when I tried it, the plot is showing empty.
Here is the code I used to plot. Could anyone help me with this.
Thanks in advance
clc
syms f(x,y)
n = 8;
a1 = 1.0086*y - 0.9216*(x - y);
b1 = 1.0107*(-x) - 1.0086*(y);
c1 = 0.9216*(x - y) - 1.0107*(-x);
h1 = 0.5877*(161.65);
I3 = ((a1.* b1.*c1)/(54))-((b1.*(h1.^2))/(6));
I2 = ((h1.^2)/(3))+((a1.^2 + b1.^2 + c1.^2)/(54));
th = acos(I3/(I2.^(3/2)));
v1 = ((2*th)+pi)/6;
an1 = (abs(2*cos(v1)))^n;
an2 = (abs(2*cos((2*th+3*pi)/6)))^n;
an3 = (abs(2*cos((2*th+5*pi)/6)))^n;
f(x,y) = ((3*I2).^(n/2)) * (an1 + an2 + an3) - (2*(189.32)^8);
fimplicit(f)

请先登录，再回答此问题。

采纳的回答

Torsten
Torsten 2019-2-11
function main
fimplicit (@(x,y)f(x,y))
end
function fun = f(x,y)
n = 8;
a1 = 1.0086*y - 0.9216*(x - y);
b1 = 1.0107*(-x) - 1.0086*(y);
c1 = 0.9216*(x - y) - 1.0107*(-x);
h1 = 0.5877*(161.65);
I3 = ((a1.* b1.*c1)/(54))-((b1.*(h1.^2))/(6));
I2 = ((h1.^2)/(3))+((a1.^2 + b1.^2 + c1.^2)/(54));
th = acos(I3./(I2.^(3/2)));
v1 = ((2*th)+pi)/6;
an1 = (abs(2*cos(v1))).^n;
an2 = (abs(2*cos((2*th+3*pi)/6))).^n;
an3 = (abs(2*cos((2*th+5*pi)/6))).^n;
fun = ((3*I2).^(n/2)).* (an1 + an2 + an3) - (2*(189.32)^8);
end
Resonable limits for plotting are required - no zeros are found in the default range [-5:5] for x and y.
  6 个评论
显示 4更早的评论
Jay
Jay 2019-2-11
编辑：Jay 2019-2-11
Hello Torsten
It works. But it is not working with other limits. Can you explain why so?
Thank you.
Torsten
Torsten 2019-2-11
It "works" as long as the object is contained in the box defined by the specified limits for x and y.

请先登录，再进行评论。

更多回答（1 个）

John D'Errico
John D'Errico 2019-2-11
编辑：John D'Errico 2019-2-11
Easy enough. Try this, for example.
vpasolve(f(1,y))
ans =
-80.224189505722446658042301607259
vpasolve(f(-20,y))
ans =
63.634253282860063957543062643774
Hmm. So [1,-80] is roughly a solution. That should be a good hint as to where to have fimplicit look.
fimplicit(f,[-150,150,-150,150])
axis equal
grid on
The problem was fimplicit looks by default in a rather narrow set of limits on x and y. It cannot know where it SHOULD be looking, and computer programs can sometimes be so clueless. Since fimplicit just found no solutions at all in the domain it was looking by default, you saw an empty figure. Sometimes you need to give even a computer a nudge in the right direction.

类别

在 Help Center 和 File Exchange 中查找有关 2-D and 3-D Plots 的更多信息

标签

产品


版本

R2018b

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by