Matlab : ODE15s Matrix is singular, close to singular or badly scaled. Results may be inaccurate. RCOND = NaN

1
votes

I'm trying to solve a system of DAE (mixture of ODE and Algebraic Eq). So, my system looks like this

M dy/dt = F(t,y)

The matrix M is basically a constant mass matrix 1 in the diagonal with all zeros on the few last lines and few last column.

so for an example mass matrix looks like this

M = [1 0 0 0 0 1 0 0 0 0 1 0 0 0 0 0]

my vector Fx is in dimension (4x1) if we take the matrix example.

How do I proceed if I get this error?

Matrix is singular, close to singular or badly scaled. Results may be inaccurate. RCOND = NaN

my code for the system resolution :

Mass = Mass_Matrix( Nc,NT );

opt = odeset('RelTol', 10.0^(-3), 'AbsTol' , 10.0^(-3), 'Mass', Mass ,'MassSingular', 'yes', 'OutputFcn',@odeprint);

[T,Y] = ode15s(@(t,y)Function_Fx( t, y, Resolution, y01),[0 1],y0,opt);

and my vector Fx is created by the Function_Fx 

function Fx = Function_Fx( t, y, Resolution, y01)

With Resolution being a struct variables, and y01 a stored values.

My question is where could be the problem, is it the F(t,y) or the M? Given M is constant mass matrix.

Thank you for your help

1
matlabmatrixode
please post a complete example with definition of Function_Fx and values for all used variables (Mass, t, y, Resolution, y01, y01). otherwise no one can reproduce your problem – m.s.
My question is where could be the problem, is it the F(t,y) or the M? Given M is constant mass matrix. – S. A.
Well, you M is singular, so quite clearly the problem is M. Simply put, your differential equation system does not specify the derivative of the y(4). – A. Donda

1 Answers

0
votes

I've solved this problem. It was because my F(t,y) is wrong. I checked the jacobian only by then I managed to see that I have some lines of zeros.