Introduce validity cascade and appropriate on-screen representation

[grumpyinca]

Recent discussion of #914 turned to an examination of the more general case and how best to represent similar situations to the user.

Consider the example where the model of a compression spring is allowed to go below the solid condition so as to avoid the numerical difficulties associated with limiting deflection at solid. In this situation, values of multiple dependent variables are no longer correct (realistic). Entire chains of dependent variables may be affected. Again, looking at a compression spring where the value of Force_2 drives the spring below the solid condition, dependent variables like L_2, Deflect_2, OD_2, ID_2, Stress_2, FS_2, FS_Cycle_Life, L_Stroke, Cycle_life, %_Avail_Deflect and Energy all become incorrect, invalid or unrealistic. Other values on the reports may be impacted as well.

Note that some of these incorrect, invalid or unrealistic conditions are covered by existing alerts.

What is the best calculation approach ? Should there be a Force_2 independent variable that is set by the user and or Search but an "Effective Force_2" that is forced to NaN if it exceeds force_Solid ?

How should the situation be communicated to the user ?

• Force value to zero
• "NA" or "N/A", "invalid", "Not applicable" or "Not appropriate"
• "Not computable"
• "See alerts" or a Link to the associated alert
• purple text
• an icon or other graphic
• row of question marks
• as above with tooltip