Simulink Error "Derivative input -47 ..." with integrator block

Hello Everybody,

I hope somebody can help me, because I cannot find a solution to my Problem. In a rather big Simulink Model I am using an Integrator Block. The Integrator Input Signal is give from a Merge Block - I have been plotting this Signal via a scope: the Input Signal is continually Zero!

Additionally I have an external Initial Condition Port - this Port is continually 100.

So the Integrator should normally do nothing - integrate 0 the the Initial value of 100. When I copy this Subsystem to a new file and put the vales manually, it works as it should - and the result is continually 100.

When I try running the model, I get the very confusion error message: Derivative input -47 of 'NameOfBlock' at time 0.08 is Inf or NaN. Stopping simulation. There may be a singularity in the solution. If not, try reducing the step size (either by reducing the fixed step size or by tightening the error tolerances)

I have already tried to put a Saturation to the Input port - with no results. Also I have tried in the Configuration Parameters - Data Import/Export - Save to Workspace - to plot the States. There I get 56 States and 2 of These becom 1e+16 , is this already Inf? But I cannot define, which state this is.

Why is it, that I get an error message with Input Port Nr. -47 ?!?!

Can anybody give my a tipp, how to locate the error?

I would be very gratefull ...

[Kaustubha Govind]

Perhaps you can try using the Simulink Debugger to understand where the model diverges?

Answer 1

[Guy Rouleau]

The port "-47" is a bug. I would recommend recommend trying in R2013b (I think it is fixed in this latest release). Also, you can contact technical support to get more information on this bug.

A few things you can try to debug your NaN error:

- Log the states in structure format, that way you will have a block name associated with the values.

- As recommend by Kaustubha, use the debugger. You have the possibility to put a breakpoint ofn Nan, which should help identifiy where this all starts.

- You might want to try this central submission to see what happens between two steps of the simulink solver:

http://www.mathworks.com/matlabcentral/fileexchange/22695-minor-time-step-logging

Answer 2

[Bettina]

Hallo back and thanks for the two answers,

I have tried the Simulink Debugger and there I found the NaN Breakpoint. I tried with the conditional breakpoint on the Signal itself, but Simulink would not allow this.

The Statement that the port "-47" is a bug, was really usefull, because I startet banging my head angainst the wall with this Integrator block.

The Debugger showed my insted, that a completly different Block was running out of an look up table data-range. How it ended up with this error report, I still can't see.

But now I fixed the look Up table and it runs fine. Thanks again!