Method newStep

SRC/analysis/integrator/TRBDF3.cpp:89–174

int TRBDF3::newStep(double deltaT)
{
    // check the vectors have been created
    if (U == 0)  {
        opserr << "TRBDF3::newStep() - domainChange() failed or hasn't been called\n";
        return -3;	
    }

    // mark step as Trapezoidal (=0), Backward Euler (=1), or Houbolt (=2)
    if (deltaT != dt || step == 2) {
        step = 0;
    } else if (step == 0) {
        step = 1;
    } else {
        step = 2;
    }

    // get a pointer to the AnalysisModel
    AnalysisModel *theModel = this->getAnalysisModel();

    // set response at t to be that at t+deltaT of previous step
    dt = deltaT;

    (*Utm2) = *Utm1;
    (*Utm2dot) = *Utm1dot;

    (*Utm1) = *Ut;
    (*Utm1dot) = *Utdot;

    (*Ut) = *U;        
    (*Utdot) = *Udot;  
    (*Utdotdot) = *Udotdot;

    // set the constants
    if (step == 0)  { // trapezoidal
        c1 = 1.0;
        c2 = 2.0/deltaT;
        c3 = 4.0/(deltaT*deltaT);

        (*Udot) *= -1.0;

        double a3 = -4.0/deltaT;
        double a4 = -1;
        Udotdot->addVector(a4, *Utdot, a3);

    } else if (step == 1)  {  // backward euler
        c1 = 1.0;
        c2 = 1.5/deltaT;
        c3 = 2.25/(deltaT*deltaT);

        (*Udot) = *Utm1;
        Udot->addVector(0.5/deltaT, *Ut, -1/(2.0*deltaT));

        (*Udotdot) = *Utm1dot;
        Udotdot->addVector(0.5/deltaT, *Utdot, -4.0/(2.0*deltaT));    
        Udotdot->addVector(1.0, *Udot, 3.0/(2.0*deltaT));    

    } else {   // Houbolt