# About the node numbering problem when calculix interacts with other software

Hello, I have some questions about the node number of calculix.
As two different software have different node numbering rules, I would like to ask what is calculix’s numbering rules for triangular mesh? (I see the manual says to number the nodes at both ends before the boundary ends in the middle?) The node numbering rule of the software I used to interact with calculix is given node number according to the sequence of nodes appearing in the imported stl file. So does anyone have any idea on how to make the node numbering of the two software be the same?

You would have to write a conversion script to convert the one sequence into the other.

In general, I would say that an STL file is not very well suited as the basis for FEA. Conversion to STL can generate really elongated triangles with wildly different sizes.

The conversion script must know the coding rules of two different pieces of software.For my fluid processing software, the code rule is to read the order in which nodes appear in the stl file. But for the S3 or S6 unit of Calculix, where do I check its coding rules?It’s better to explain and code.

In the `*ELEMENT` command, nodes are simply listed from first to last.
(in the example shown below: 1, 2, 3, 4, 5, 6)

Look at the documentation for the element types to see how those are arranged geometrically. For S6:

S6 for an element I know it looks like this. But for many elements, why does calculix choose to label the nodes at both ends 1,2 first? And then label the boundary, and finally label the points inside? (When using the S6)

I guess that is because you can generate second order elements from first order elements without having to renumber the existing nodes.

Anyways, it is dictated by ABAQUS file format.

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