double [] getCalc(double t, int K, int I){
        double hx2=Math.pow(hx, 2);
        this.ht=t/K;
        this.hx=l/I;
        this.I=I;
        double a_=a2*(theta-1)*ht;
        double b_=2*(1-theta)*a2*ht+(theta-1)*ht*hx2*b;
        double c_=a_+b_;


        double a__=a2*theta*ht;
        double b__=hx2-2*a2*theta*ht+theta*ht*hx2*b;
        double [] F = new double [I-1];
        double [] U = null;
        for (int k=0; k<K; k++)
        {
            if (k==0)
                for (int i=0; i<I-1; i++)
                F[i]=a__*this.getPsi(i*hx)+b__*this.getPsi((i+1)*hx)+
                     a__*this.getPsi((i+2)*hx)+ht*hx2*this.getPhi((i+1)*hx);
            else
                for (int i=0; i<I-1; i++){
                    if (i==0)
                        F[i]=a__*U[i]+b__*U[i]+a__*U[i+1]+
                             ht*hx2*this.getPhi((i+1)*hx);
                    if (i==I-2)
                        F[i]=a__*U[i-1]+b__*U[i]+a__*U[i]+
                             ht*hx2*this.getPhi((i+1)*hx);
                    if ((i>0) && (i<I-2))
                        F[i]=a__*U[i-1]+b__*U[i]+a__*U[i+1]+
                             ht*hx2*this.getPhi((i+1)*hx);
                }
            double [] P = new double [I-2]; //n-1

            P[0]=a_/(a_+b_);
            F[0]=-F[0]/(a_+b_);
                for (int i=1; i<I-1; i++){
                if (i<I-2)
                    P[i]=a_/(b_-P[i-1]*a_);
                F[i]=(F[i]-F[i-1]*a_)/(b_-P[i-1]*a_);
            }
            for (int i=I-2; i>0; i--){
                F[i-1]=F[i-1]-P[i-1]*F[i];
            }
            U=F.clone();
        }


       return U;
    }