Im getting the Error using inv Matrix must be square. error.

Question

Tyler Dennis 2014-10-20

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/159323-im-getting-the-error-using-inv-matrix-must-be-square-error

编辑： SK 2014-10-21

Essentially i have to plot the acceleration of a point on a linkage with respect to theta 2 or in my code, t2, but due to complicated vector loops my equations are slightly complex. When I solve for my w4 and f_dot values using single values all is well and good but when i go to plot them using a varying theta, i get an error about my matrix not being square.

Here is my code

%givens

a=1;

b=4;

c=8;

d=1.3;

k=0.3;

g=5;

w2=20;

alpha2=0

t2=0:10

%position variables

t4=atan((a*sin(t2)+k)/(a*cos(t2)+d))

f=(a*cos(t2)+k)/cos(t4)

%velocity loop one

A=[-cos(t4), f*sin(t4); -sin(t4), -f*sin(t4)]

B=[a*w2*sin(t2); -a*cos(t2)]

C=inv(A);

D=C*B;

f_dot=C(1)

w4=C(2)

any help would be greatly appreciated. thank you

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Jan 2014-10-21

编辑：Jan 2014-10-21

Please format your code properly.

When you describe an error, be sure to post a copy of the complete message.

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Answer 1

SK 2014-10-20

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/159323-im-getting-the-error-using-inv-matrix-must-be-square-error#answer_155852

编辑：SK 2014-10-20

在 MATLAB Online 中打开

Instead of:

t4=atan((a*sin(t2)+k)/(a*cos(t2)+d))
f=(a*cos(t2)+k)/cos(t4)

did you mean:

t4=atan((a*sin(t2)+k)./(a*cos(t2)+d))
f=(a*cos(t2)+k)./cos(t4)

using A/B when arguments are vectors or matrices will result in Matlab trying to solve the equation xB = A (by means of least squares) In this case it will be a scalar least squares solution to an overdetermined system. Is that what you want? If you want element by element division use "./".

Also in:

A=[-cos(t4), f*sin(t4); -sin(t4), -f*sin(t4)]

A is a (2 x 11) matrix, since f is a (1 x 10) vector. So A is not square.

It may be easier to write the code using loops first. You can vectorize it later. My guess is that you probably want the following:

a = 1;
b = 4;
c = 8;
d = 1.3;
k = 0.3;
g = 5;
w2 = 20;
alpha2 = 0
t2 = 0 : 10
t4 = atan((a*sin(t2)+k)./(a*cos(t2)+d))
f = (a*cos(t2)+k)./cos(t4)
N = length(t2);
f_dot(1,N) = 0;
w4(1,N) = 0;
for i = 1 : N
  A = [-cos(t4(i)), f(i)*sin(t4(i)); -sin(t4(i)), -f(i)*sin(t4(i))]
  B = [a*w2*sin(t2(i)); -a*cos(t2(i))]
  C = inv(A);
  D = C*B;
  f_dot(i) = C(1)
  w4(i) = C(2)
end

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Tyler Dennis 2014-10-21

在 MATLAB Online 中打开

Now the issue becomes that i start getting a 1 for all values of theta starting at the matrix containing h_dot. also known as the third for loop. Basically im plotting t2 vs apx and apy. a = 1;

b = 4;

c = 8;

d = 1.3;

k = 0.3;

g = 5;

w2 = 20;

alpha2 = 0

t2 = 0 : 360

t4 = atan((a*sin(t2)+k)./(a*cos(t2)+d));

t5 = asin((b*sin(t4)-g)./g);

f = (a*cos(t2)+k)./cos(t4);

h = c*cos(t5)-b*cos(t4);

N = length(t2);

f_dot(1,N) = 0;

w4(1,N) = 0;

for i = 1 : N

A = [-cos(t4(i)), f(i)*sin(t4(i)); -sin(t4(i)), -f(i)*sin(t4(i))]
B = [a*w2*sin(t2(i)); -a*cos(t2(i))]
C = inv(A);
D = C*B;
f_dot(i) = C(1)
w4(i) = C(2)

end

for i = 1 : N

A = [-cos(t4(i)), f(i)*sin(t4(i)); -sin(t4(i)), -f(i)*sin(t4(i))]
B = [a*alpha2*sin(t2(i))+a*(w2^2)*cos(t2(i))-2*f_dot(i)*w4(i)*sin(t4(i))-f(i)*(w4(i)^2)*cos(t4(i));
    -a*alpha2*cos(t2(i))+a*(w2^2)*sin(t2(i))+2*f_dot(i)*w4(i)*cos(t4(i))-f(i)*(w4(i)^2)*sin(t4(i))];
C = inv(A);
D = C*B;
f_ddot(i) = C(1)
alpha4(i) = C(2)

end for i = 1 : N

A = [c*sin(t5(i)), 1; -c*cos(t5(i)), 0];
B = [b*w4(i)*sin(t4(i)); -b*w4(i)*cos(t4(i))];
C= inv(A)
D = C*B
w5(i) = C(1)
h_dot(i) = C(2)  
end
for i = 1 : N
A = [c*sin(t5(i)), 1; -c*cos(t5(i)), 0];
B = [b*alpha4(i)*sin(t4(i))+b*((w4(i))^2)*cos(t4(i))-c*((w5(i))*cos(t5(i))); -b*alpha4(i)*cos(t4(i))+b*((w4(i))^2)*sin(t4(i))-c*((w5(i))*cos(t5(i)))];
C = inv(A);
D = C*B;
alpha5(i) = C(1)
h_dot(i) = C(2)

end

for i=1:N

    Ax=-b*alpha4(i)*sin(t4(i))-b*((w4(i))^2)*cos(t4(i))+0.5*c*alpha5(i)*sin(t5(i))+0.5*c*((w5(i))*cos(t5(i)));
    apy=b*alpha4(i)*cos(t4(i))-b*((w4(i))^2)*sin(t4(i))-0.5*c*alpha5(i)*cos(t5(i))+0.5*c*((w5(i))*cos(t5(i)));
end

plot(t2,Ax)

plot(t2,apy)

Jan 2014-10-21

@Tyler and SK: Your code would be much easier to read, when you format it properly. The additional white lines after each line of code are counter productive.

SK 2014-10-21

@Jan

Hi. Thanks for the suggestion. Do note that usually I take great care to format the code. In this case what I wrote was strictly not code and hence I wrote it as text. However I formatted the matrix as code for easy readability. In text mode, there doesn't seem to be any way to go to the next line - its either same line or skip one line.

Regards.

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