When solving a large (N ~ 1000) system of Differential Algebraic Equations (DAEs) using the "ode15s" solver, I encountered an error "This DAE appears to be of index greater than 1". This error seems to be generated only when the value of a parameter "A" in the model equations is changed from 1e-10 to 1e-12. The system of equations is solved successfully when A = 1e-10, however when A=1e-12, the DAE error is generated.
Why does the index of equations become greater than 1 when the parameter value is changed?
Do you have any suggestions as to how to solve this issue ?
I am using the following options to solve my system of DAEs –
options = odeset('Mass',M,'MassSingular','yes','RelTol',1e-4,'AbsTol',1e6,'OutputFcn',@odetpbar);[tout, yout] = ode15s(@f_pdes,tspan,y,options);
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