_OBJECT-ORIENTED FINITE-ELEMENT SOFTWARE_
by Al Vermeulen

[LISTING ONE]

class Func {
public:
 virtual ~Func() {};
 virtual double evaluate(double x)                const =0;
 virtual double evaluate(double x,  int d)        const;
         double operator()(double x)              const {return evaluate(x);}
         double operator()(double x,int d)        const {return evaluate(x,d);}
 virtual DoubleVec operator()(const DoubleVec& x) const;
 virtual DoubleVec operator()(const DoubleVec& x, const IntVec& d) const;
 virtual DoubleVec operator()(double x, const IntVec& d) const;
};



[LISTING TWO]

void plot(const Func& f, double a, double b, double step)
{
  moveto(a,f(a));
  for(double x=a+inc; x<=b; x+=step) {
    drawto(x,f(x));
  }
  drawto(b,f(b));
}


[LISTING THREE]

FuncHandle dudx = diff(u,x);
FuncHandle dwdx = diff(w,x);
FuncHandle dNidx = diff(Ni,x);
FuncHandle integrand = EA*(dudx+dwdx*dwdx/2)*dNidx;
double fi = I(integrand);   // I is an instance of the GQuad class



[LISTING FOUR]

class NLSys
{
  public:
    virtual DoubleVec value(const DoubleVec& x) =0;
      // Calculate K(x).
    virtual int setKt(const DoubleVec& x) =0;
      // Evaluate the tangent stiffness matrix at the point "x".
      // Subsequent calls to solveTangentSystem should use the
      // tangent stiffness matrix as set here. If the tangent 
      // stiffness matrix is singular at this point then return a
      // 0 and do nothing, otherwise return a 1.
    virtual DoubleVec solveTangentSystem(const DoubleVec& b) =0;
      // Solve the system Ku=b for u where K is the last calculated
      // tangent stiffness matrix.  u and b are increments.
};