Error with a node listed under "in cascade: zero coefficient on the dependent side of an equation"

General Questions
1

I thought about putting this under tips and tricks, but maybe Bug could be more reasonable.

I let the tool search for a tie pair and it kept getting that error. I found that I could create a node set by node ID to identify the node giving the error. I noticed that the only MPC in that node was the Tie so I deleted it and made it by hand and that resolved the problem.

I found this in one of the online manuals:

*DISTRIBUTING COUPLING,ELSET=E1
LOAD,1.
*DISTRIBUTING COUPLING,ELSET=E2
LOAD2,1.
*NSET,NSET=LOAD
5,6,7,8,22,25,28,31,100
*NSET,NSET=LOAD2
8,28,100,31,5
will not work because the dependent nodes 5 and 8 are used as independent nodes as well in EACH of the distributing coupling definitions. An error message will result in the form:

*ERROR in cascade: zero coefficient on the
dependent side of an equation
dependent node: 5

Since node 5 is used into cases, it gives an error. I know of this happens when you apply for example rigid constrains to nodes. It would be cool to have a full list of possible issues related to shared nodes.

2

The Bug Reports section is meant for PrePoMax bugs to be resolved so I moved this to General Questions.

Overconstraints are indeed quite often an issue when working with CalculiX. Especially with tie constraints involved.

3

I suppose it would be a Calculix request, but I would love to see in the result something like:

Node 5 is highlighted, it belongs to Constraint1 and constraint 2, thus causing the error. Then an Elset is highlighted and I can get a quick understanding of what I did wrong.

4

I think such functionality would be great, but there are many scenarios when such CalculiX errors arises. So it will be difficult to capture all of them inside PrePoMax.

Version v1.4.0 of PrePoMax has a feature to search/find items by ids: Tools->Find, where their ids can be used to easily find the items.

image

2 Likes
5

yup that’s how I figured it out. I used the ID values to find the culprit nodes.