"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)

%% 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

[Eileen Endres]

Any help would be much appreciated.

[G A]

th4g=45*deg2rad; 

what is it? Must be

th4g=deg2rad(45);

and the others in a similar way

Answer 1

[Sai Sumanth Korthiwada]

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.