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h2. What do numerical instability warnings indicate?

*Answer:* Numerical instability warnings indicate that digits of accuracy were lost during computation. {new-tab-link:http://www.csiberkeley.com/}CSI{new-tab-link} Software performs computation with 16 digits of accuracy, some of which may be lost when analysis involves systems of significantly different stiffness, wherein which lower-order values are truncated to suit operations with higher-order values. When this warning occurs, [ETABS|etabs:Home] reports the location of the occurrence such that the user may edit the model if necessary.

Some situations where numerical instability may occur include:

* When [frame|kb:Frame] objects of significantly different stiffness connect at a common [joint|kb:Joint].

* When the rigid-diaphragm assumption is applied to a slab with flexible interconnecting objects. 

* When multiple releases are assigned to a joint, causing joint DOF to become orphaned (without stiffness). In this instance, numerical instability warnings indicate a modeling problem which should be corrected.

Depending on the number of digits lost, actions which result include the following:

* *Less than 6* does not generate a response in that values and solution are sufficiently accurate.

* *Between 6 and 11* lost digits of accuracy may or may not create numerical problems, therefore warning message is reported which reads: The results of the analysis may still be acceptable but the user should carefully check the results, especially the global sums of loads.

* *Over 11* digits lost causes analysis to terminate because results may not be sufficiently accurate. ETABS indicates the location of the numerical problem, and presents a warning message which prompts the user to check and revise the model.