# Solver-Related Warnings and Error Messages

The following section extends "Troubleshooting: What should I do if...".It describes the handling with warnings, error messages and selected problems occurring during the simulation with BDF and MEBDF. For debugging and troubleshooting it is recommended to repeat the following sections of section "Analysis".

and to know the used terminology .

The following pre-determinations are valid

• Tracing can be activated as described in the section on tracing. The relevant tracing item will be referred by its name, e.g. Solver/States
• The use of the parameter `traceOn` is described in the section "Tracing".
• See "Solver Settings" for further simulation parameters of menu Simulation/Transient Settings…/Solver/Further Parameters. The relevant parameters are referred to by their names, e.g. `dblResRelError`.

## Fixed-Step Solver and CVODE Warnings

Quantities which are computed simultaneously inside so called blocks are a particularity of . These blocks correspond to systems of linear or non-linear equations which are solved by a variant of the (iterative) Newton method. The solution can sometimes fail. Then the following error message occurs.

An error message follows the above output. It tells us when the error occurs (during the initialization, at an integration step, during the reinitialization after a discontinuity, etc.). That is important to find the block equations inside the tracing Equations/Symbolic Jacobian. In most cases one of the following four messages will be displayed before the above error message. They give us more detailed indications why the solution of the block equations fails.

E.g. inconsistent initial values can be the reason for the output of this message during the initialization:

21. Step: Residual is not in the image of 2*1-Jacobian with the DAE state _der_connection3.phi: res = 6.5741692360397401 (>4.4408920985006302e-013) != jac * s = 1 * 0

Two error messages follow:

Error: System of equations with the DAE state(s) _der_connection3.phi cannot be solved! After 21 steps residual is not in the image of the Jacobian.

Calculation aborted because of a problem during the calculation of initial conditions.

Consider the block equations and the initial values of the involved variables (several equations have been combined) inside the output of the tracing Equations/Symbolic Jacobian.

``````initial: connT.om0.fixed:=true;;
initial: connection3.om0.fixed:=true;
initial: der_connection3.phi=connection3.om.start=connection3.om0=0;
initial: der_connT.phi=connT.om.start=connT.om0=20;
initial:{{
EQUATION<>{_der_connection3.phi=0.65741692360397397*_der_connT.phi}
EQUATION<>{_der_connection3.phi=connection3.om.start}
}};``````

Then we can easily identify the cause of the problem here: the given initial values were fixed and are inconsistent.

Currently, the values of all variables can only be examined by opening a result window (`dtProtMin` should be sufficiently small). If the quantity is not directly accessible, a general function element (f(x) in the Signal Blocks library) may be used. Then its name must be entered as expression of the general function block.