How to fix this code

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karimat bello
karimat bello 2018-7-20
评论： Aquatris 2018-7-20
function [Centriod, M_Inertia,cpmo]=Rect(x,y)
if ~isequal(size(x),size(y))
error('X and Y must be the same size');
end
xm=mean(x);
ym=mean(y);
x=x-xm;
y=y-ym;
xp=x([2:end 1]);
yp=y([2:end 1]);
a=x.*yp-xp.*y;
A=sum(a)/2;
xc=sum((x+xp).*a)/6/A;
yc=sum((y+yp).*a)/6/A;
Ixx=sum((y.*y+y.*yp+yp.*yp).*a)/12;
Iyy=sum((x.*x+x.*xp+xp.*xp).*a)/12;
Ixy=sum((x.*yp+2*x.*y+2*xp.*yp+xp.*y).*a)/24;
dx=xp-x;
dy=yp-y;
P=sum(sqrt(dx.*dx+dy.*dy));
if A<0
A=-A;
Ixx=-Ixx;
Iyy=-Iyy;
Ixy=-Ixy;
end
Iuu=Ixx-A*yc*yc;
Ivv=Iyy-A*xc*xc;
Iuv=Ixy-A*xc*yc;
J=Iuu+Ivv;
x_cen=xc+xm;
y_cen=yc+ym;
Ixx=Iuu+A*y_cen*y_cen;
Iyy=Ivv+A*x_cen*x_cen;
Ixy=Iuv+A*x_cen*y_cen;
I=[Iuu -Ivv;
-Iuv Ivv];
[eig_vec, eig_val]=eig(I);
I1=eig_val(1,1);
I2=eig_val(2,2);
ang1=atan2(eig_vec(2,1),eig_vec(1,1));
ang2=atan2(eig_vec(2,2),eig_vec(1,2));
Centriod=[A x_cen y_cen P];
M_Inertia=[Ixx Iyy Ixy];
cpmo=[I1 ang1 I2 ang2 J];
end
Error using eig
Input to EIG must not contain NaN or Inf.
Error in Rect (line 46)
[eig_vec, eig_val]=eig(I);

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回答（1 个）

Aquatris
Aquatris 2018-7-20
编辑：Aquatris 2018-7-20
In these lines;
xc=sum((x+xp).*a)/6/A
yc=sum((y+yp).*a)/6/A
when A is 0, these values become NaN since division by 0 is not defined. Since they are NaN, any other variable that uses them become NaN as well. eig() function requires numeric values since there cannot be eigenvalues of NaN.
If in your application A can be 0, these equations do not seem to be right. Otherwise, if A can be 0 and the equations are right, you can use an if statement to force xc and yc to be some number when A is equal to 0.
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karimat bello
karimat bello 2018-7-20
The error message is coming from eig() not from the value of A.
Aquatris
Aquatris 2018-7-20
Correct but the underlying reason is the variable A. Since A is NaN, the other variables that are calculated using the A variable becomes NaN as well. Then you feed a matrix with NaN elements to eig() function, which is where you see the error since eig() function cannot work with NaN.
To test this, you can replace the equation that is "A = sum(a)/2" withs "A = 5" or any other numeric value, and you will see your code runs fine.

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