大型稀疏矩阵的形式：程序代码运行带这一段就终止了，检查好几遍，看不不出错误，求指点！


for(i=0;i<(P+1)*(N+1);i++)
coefficients.push_back(Tri(i,i,1.0));  //第一个i表示A矩阵中的行数，第二个i表示A矩阵中的列数，1.0表示非零元素的系数
    //矩阵A中的中间行

    for(i=(P+1)*(N+1);i<SMADi-(P+1)*(N+1);i++)
    {
        k=i%(P+1)*(N+1);
        
        //矩阵A中每一个B矩阵中的首行

        for(k=0;k<P+1;k++)
        {
            //矩阵B中首行的每一个a矩阵中的首行
            if(k==0)   
            {
                coefficients.push_back(Tri(i,i,-6.0));
                coefficients.push_back(Tri(i,i+1,2.0));
                coefficients.push_back(Tri(i,i+(P+1),2.0));
                coefficients.push_back(Tri(i,i-(P+1)*(N+1),1.0));
                coefficients.push_back(Tri(i,i+(P+1)*(N+1),1.0));
            }

            //矩阵B中首行的每一个a矩阵中的末行
            
            else if(k==P)
            {
                coefficients.push_back(Tri(i,i,-6.0));
                coefficients.push_back(Tri(i,i-1,2.0));
                coefficients.push_back(Tri(i,i+(P+1),2.0));
                coefficients.push_back(Tri(i,i-(P+1)*(N+1),1.0));
                coefficients.push_back(Tri(i,i+(P+1)*(N+1),1.0));
            }

            //矩阵B中首行的每一个a矩阵中的中间行
            
            else
            {
                coefficients.push_back(Tri(i,i,-6.0));
                coefficients.push_back(Tri(i,i-1,1.0));
                coefficients.push_back(Tri(i,i+1,1.0));
                coefficients.push_back(Tri(i,i+(P+1),2.0));
                coefficients.push_back(Tri(i,i-(P+1)*(N+1),1.0));
                coefficients.push_back(Tri(i,i+(P+1)*(N+1),1.0));
            }

        }
        //矩阵A中每一个B矩阵中的中间行

        for(k=P+1;k<N*(P+1);k++)
        {
            for(int m=1;m<N;m++)
            {
            //矩阵B中首行的每一个a矩阵中的首行

                if(k==m*(P+1))
                {
                coefficients.push_back(Tri(i,i,-6.0));
                coefficients.push_back(Tri(i,i+1,2.0));
                coefficients.push_back(Tri(i,i-(P+1),1.0));
                coefficients.push_back(Tri(i,i+(P+1),1.0));
                coefficients.push_back(Tri(i,i-(P+1)*(N+1),1.0));
                coefficients.push_back(Tri(i,i+(P+1)*(N+1),1.0));
                }

            //矩阵B中首行的每一个a矩阵中的末行
               
                else if(k==m*(P+1)+P)
                {
                coefficients.push_back(Tri(i,i,-6.0));
                coefficients.push_back(Tri(i,i-1,2.0));
                coefficients.push_back(Tri(i,i-(P+1),1.0));
                coefficients.push_back(Tri(i,i+(P+1),1.0));
                coefficients.push_back(Tri(i,i-(P+1)*(N+1),1.0));
                coefficients.push_back(Tri(i,i+(P+1)*(N+1),1.0));
                }

            //矩阵B中首行的每一个a矩阵中的中间行
            
                else
                {
                coefficients.push_back(Tri(i,i,-6.0));
                coefficients.push_back(Tri(i,i-1,1.0));
                coefficients.push_back(Tri(i,i+1,1.0));
                coefficients.push_back(Tri(i,i-(P+1),1.0));
                coefficients.push_back(Tri(i,i+(P+1),1.0));
                coefficients.push_back(Tri(i,i-(P+1)*(N+1),1.0));
                coefficients.push_back(Tri(i,i+(P+1)*(N+1),1.0));
                }
            }

        }

        //矩阵A中每一个B矩阵中的末行

        for(k=N*(P+1);k<(N+1)*(P+1);k++)
        {
        
            //矩阵B中首行的每一个a矩阵中的首行

            if(k==N*(P+1))   
            {
                coefficients.push_back(Tri(i,i,-6.0));
                coefficients.push_back(Tri(i,i+1,2.0));
                coefficients.push_back(Tri(i,i-(P+1),2.0));
                coefficients.push_back(Tri(i,i-(P+1)*(N+1),1.0));
                coefficients.push_back(Tri(i,i+(P+1)*(N+1),1.0));
            }

            //矩阵B中首行的每一个a矩阵中的末行
            
            else if(k==(N+1)*(P+1)-1)
            {
                coefficients.push_back(Tri(i,i,-6.0));
                coefficients.push_back(Tri(i,i-1,2.0));
                coefficients.push_back(Tri(i,i-(P+1),2.0));
                coefficients.push_back(Tri(i,i-(P+1)*(N+1),1.0));
                coefficients.push_back(Tri(i,i+(P+1)*(N+1),1.0));
            }

            //矩阵B中首行的每一个a矩阵中的中间行
            
            else
            {
                coefficients.push_back(Tri(i,i,-6.0));
                coefficients.push_back(Tri(i,i-1,1.0));
                coefficients.push_back(Tri(i,i+1,1.0));
                coefficients.push_back(Tri(i,i-(P+1),2.0));
                coefficients.push_back(Tri(i,i-(P+1)*(N+1),1.0));
                coefficients.push_back(Tri(i,i+(P+1)*(N+1),1.0));
            }

        }
        
    }

    //矩阵A中的末行

    for(i=SMADi-(P+1)*(N+1);i<SMADi;i++)
    {
        //B矩阵中的首行

        for(i=SMADi-(P+1)*(N+1);i<SMADi-(P+1)*N;i++)
        {
            if(i==SMADi-(P+1)*(N+1))
            {
                coefficients.push_back(Tri(i,i,-6.0));
                coefficients.push_back(Tri(i,i+1,2.0));
                coefficients.push_back(Tri(i,i+(P+1),2.0));
                coefficients.push_back(Tri(i,i-(P+1)*(N+1),2.0));
            }

            else if(i==SMADi-(P+1)*N-1)
            {
                coefficients.push_back(Tri(i,i,-6.0));
                coefficients.push_back(Tri(i,i-1,2.0));
                coefficients.push_back(Tri(i,i+(P+1),2.0));
                coefficients.push_back(Tri(i,i-(P+1)*(N+1),2.0));
            }

            else
            {
                coefficients.push_back(Tri(i,i,-6.0));
                coefficients.push_back(Tri(i,i-1,1.0));
                coefficients.push_back(Tri(i,i+1,1.0));
                coefficients.push_back(Tri(i,i+(P+1),2.0));
                coefficients.push_back(Tri(i,i-(P+1)*(N+1),2.0));
            }
            
        }
        //B矩阵的中间行

        for(i=SMADi-N*(P+1);i<SMADi-(P+1);i++)
        {
            for(int k=0;k<N-1;k++)
            {
                if(i==SMADi-(N-k)*(P+1))
                {
                    coefficients.push_back(Tri(i,i,-6.0));
                    coefficients.push_back(Tri(i,i+1,2.0));
                    coefficients.push_back(Tri(i,i-(P+1),1.0));
                    coefficients.push_back(Tri(i,i+(P+1),1.0));
                    coefficients.push_back(Tri(i,i-(P+1)*(N+1),2.0));
                }
                else if(i==SMADi-(N-k)*(P+1)+P)
                {
                    coefficients.push_back(Tri(i,i,-6.0));
                    coefficients.push_back(Tri(i,i-1,2.0));
                    coefficients.push_back(Tri(i,i-(P+1),1.0));
                    coefficients.push_back(Tri(i,i+(P+1),1.0));
                    coefficients.push_back(Tri(i,i-(P+1)*(N+1),2.0));
                }
                else
                {
                    coefficients.push_back(Tri(i,i,-6.0));
                    coefficients.push_back(Tri(i,i-1,1.0));
                    coefficients.push_back(Tri(i,i+1,1.0));
                    coefficients.push_back(Tri(i,i-(P+1),1.0));
                    coefficients.push_back(Tri(i,i+(P+1),1.0));
                    coefficients.push_back(Tri(i,i-(P+1)*(N+1),2.0));
                }
            }
            
        }

        //B矩阵中的末行

        for(i=SMADi-(P+1);i<SMADi;i++)
        {
            if(i==SMADi-(P+1))
            {
                coefficients.push_back(Tri(i,i,-6.0));
                coefficients.push_back(Tri(i,i+1,2.0));
                coefficients.push_back(Tri(i,i-(P+1),2.0));
                coefficients.push_back(Tri(i,i-(P+1)*(N+1),2.0));
            }

            else if(i==SMADi-1)
            {
                coefficients.push_back(Tri(i,i,-6.0));
                coefficients.push_back(Tri(i,i-1,2.0));
                coefficients.push_back(Tri(i,i-(P+1),2.0));
                coefficients.push_back(Tri(i,i-(P+1)*(N+1),2.0));
            }

            else
            {
                coefficients.push_back(Tri(i,i,-6.0));
                coefficients.push_back(Tri(i,i-1,1.0));
                coefficients.push_back(Tri(i,i+1,1.0));
                coefficients.push_back(Tri(i,i-(P+1),2.0));
                coefficients.push_back(Tri(i,i-(P+1)*(N+1),2.0));
            }
            
        }

    }

没人帮我检查一下啊！看来只能自己奋斗了!

大型稀疏矩阵的单位形式如何定义的？
说一下你定义的结构形式

如果是找矩阵A的非零系数。
A是（P+1）*（N+1）*（M+1）阶方阵
首先能不能找A中任意第i列，j行元素A(i,j)对应于a,b,c中的某行某列。
A由B、C组合而来，没有加减。系数非零和零不会互变。

谢谢你们的回复，差不多弄对了！Thank you again！