When the PDELTA ANALYSIS command is specified with the CONVERGENCE (m) parameter, the output file contains a message such as:
Load Case = 1 Convergence Error (SRSS) = 2.790E-02 INCH
What does this number represent?
The SRSS is the square root of the sum of the squares of the change in displacement (from one iteration to the next) of every dof. If after an iteration, the SRSS falls below the SET DISP tol or default tolerance thenthat PDELTA load case is converged.Mathematically this is the Euclidean norm of the vector of displacement changes.
|| {DISPi} - {DISPi-1} ||
SRSS=0.00do iDOF=1,nj6SRSS=SRSS+(dj(iDOF,ipdload)-olddj(iDOF,ipdload))**2enddoSRSS=sqrt(SRSS)
The SRSS printed is for the last iteration performed for that load case and tends to be an upper bound on the amount of error in any one displacement.