DAE Problem : cannot understand how to find the problem in my code

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Urvi
Urvi 2012-9-28
This is code to solve 6 ode's and 12 algebraic equations. All of them are interdependent. How do I go about it? I keep getting errors but I am unable to solve it.
**M file**
*M file* function f=ncs1_dae(t,x)
%Input parameters
global alpha A AH AI AO AV ACS beta CPH CPI CPIN CPO CPV dB g hB hI hO hH hV Hmax k M MH min Pset qein R rhol rhov ri ro TIN TR vB lambda;
input()
%Variables
TI=x(1);
........
..........
=x(16);
%f(1) to f(6) are ODEs
f(1)=
f(2)=
f(3)=
f(4)=
f(5)=
f(6)=
%f(7) to f(18) are Algebraic Equations
f(7)=
f(8)=
f(9)=
f(10)=
f(11)=
f(12)=
f(13)=
f(14)=
f(15)=
f(16)=
f(17)=
f(18)=
f=f';
This is what I enter in the command window:
>> x0=[298 298 298 298 1 0.3 0 373 0 0 0 0 0 0 0 0.0013 0.0041 0.0056];
>> tspan=[0 1200];
>> M=[eye(6,18);zeros(12,18)];
>> options=odeset('Mass',M);
>> [t1,x1]=ode15s(f,[0,1200],x0,options);
The warning msg I get is : Warning: Failure at t=3.014342e-01. Unable to meet integration tolerances without reducing the step size below the smallest value allowed (8.881784e-16) at time t. > In ode15s at 753 >> if true
% code
end

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回答（1 个）

Jan
Jan 2012-10-1
编辑：Jan 2012-10-1
You can define an DAE such that there is no feasible point. If the mass matrix is singular, as in your case, the initial slope M(t0, y0) * y'(0) = f(t0, y0) must exist.
Imagine a DAE which describes a point sliding on a circulare wire. If you start the integration with a point apart from the wire, there is no valid first step of the integration, because it is impossible to keep the trajectory on the feasible path.

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