"Warning: Matrix is singular, close to singular or badly scaled. Results may be inaccurate. " RCOND = NaN. I'm using Newton's Method which uses a Jacobian Matrix for space mech. class. not sure how to fix w/out changing elements of matrix (set)

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Eileen Endres
Eileen Endres 2021-2-17
编辑： Sai Sumanth Korthiwada 2022-12-20
%% Create Guess vector
th4g=45*deg2rad;
th3g=225*deg2rad;
th5g=350*deg2rad;
% [r3 ; r6 ;th3 ; th4 ; th5]
guess = [3;8;th3g;th4g;th5g];
% set up a tolerance value
t=10^-6;
error=2*t;
% Define initial and final input angle
th2_start=200*deg2rad;
th2_end=135*deg2rad;
% generate input vector
n=100;
th2=linspace(th2_start,th2_end,n)';
% matrix to hold results
guess_save = zeros(n,length(guess));
%% Jacobian
for i=1:n
while error > t
% Jacobian Matrix
J1=[-cos(guess(3)) 0 (guess(1)*sin(guess(3))) 0 0];
J2=[-sin(guess(3)) 0 (-guess(1)*cos(guess(3))) 0 0];
J3=[0 -cos(th6) 0 -r4*sin(guess(4)) -r5*sin(guess(5))];
J4=[0 sin(th6) 0 r4*cos(guess(4)) r5*cos(guess(5))];
J5=[0 0 1 -1 0];
J=[J1;J2;J3;J4;J5];
% Calculate the function values
f1=r2*cos(th2(i))-guess(1)*cos(guess(3))-r1*cos(th1);
f2=r2*sin(th2(i))-guess(1)*sin(guess(3))-r1*sin(th1);
f3=r4*cos(guess(4))+r5*cos(guess(5))-guess(2)*cos(th6);
f4=r4*sin(guess(4))+r5*sin(guess(5))-guess(2)*sin(th6);
f5=guess(4)- pi-guess(3);
% make a function vector
FUN=[f1;f2;f3;f4;f5];
% save our initial guess
guess_1=guess;
% calculate the new guess
guess= -J^-1*FUN+guess;
% calculate the error
error=max(abs(guess_1-guess));
end
% reset error
error =2*t;
% save guess value
guess_save(i,:)= guess;
end

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回答（1 个）

Sai Sumanth Korthiwada
编辑：Sai Sumanth Korthiwada 2022-12-20
Hi Eileen,
I understand that you are encountering a warning message while working on Newton’s method which uses Jacobian matrix.
Please make the following changes in your code:
%% Create Guess vector
% th4g=45*deg2rad;
% th3g=225*deg2rad;
% th5g=350*deg2rad;
%% Create Guess vector
% Use this:-
th4g=deg2rad(45);
th3g=deg2rad(225);
th5g=deg2rad(350);
Please use 'deg2rad(angle)' instead of 'angle*deg2rad' in the remaining code as well.
Refer to the documentation below for more information on 'deg2rad' function:
https://in.mathworks.com/help/matlab/ref/deg2rad.html
Hope this resolves your query.

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