matrixbase::GetLowerTriangular

GetLowerTriangular

Description

Get a lower triangular matrix from this matrix.

Syntax

int GetLowerTriangular( matrixbase & mbResult, int nNumDiagonal = 0 )

Parameters

mbResult

[output] The result matrix containing only the lower part

nNumDiagonal

[input] Default 0 is the main diagonal, > 0 is above the

main diagonal, and < 0 is below the main diagonal.

Return

Returns 0 on success and a non-zero error code on failure.

-1=Internal cast error.

Examples

EX1

void matrixbase_GetLowerTriangular_ex1()
{
    matrix<double> mat1 = {
        { 1, 1, 99,  1,  1},
        {99, 1,  1,  1,  1},
        { 1, 1,  1,  1,  1}
    };
    mat1[1][0]=NANUM;  // set row=2,col=1 to NANUM
    mat1[0][2]=NANUM;  // set row=1,col=3 to NANUM
    matrix<double> mat2;
    
        int rc = mat1.GetLowerTriangular(mat2); 
    if(rc!=0) 
        printf(" Error: GetLowerTriangular failed. Error Code=%d\n",rc);
    else{
        printf("The matrix is:\n");
        for(int ii=0; ii< mat2.GetNumRows(); ii++){
                        for(int jj=0; jj< mat2.GetNumCols(); jj++) 
                                printf("%g  ", mat2[ii][jj]);
                        printf("\r\n");
        }
    }
}

EX2

// Convert a matrix to the lower triangular matrix
void matrixbase_GetLowerTriangular_ex1()
{
    matrix<double> mat1 = {
        { 1, 1, 99,  1,  1},
        {99, 1,  1,  1,  1},
        { 1, 1,  1,  1,  1}
    };
    mat1[1][0]=NANUM;  // set row=2,col=1 to NANUM
    mat1[0][2]=NANUM;  // set row=1,col=3 to NANUM
 
//   Input matrix is:
//        { 1, 1, --,  1,  1}
//        {--, 1,  1,  1,  1}
//        { 1, 1,  1,  1,  1}
 
//   LowerTriangular matrix is:
//        { 1, 0,  0,  0,  0}
//        {--, 1,  0,  0,  0}
//        { 1, 1,  1,  0,  0}

//   LowerTriangular matrix from the 1th diagonal below the main diagonalis:
//        { 0, 0,  0,  0,  0}
//        {--, 0,  0,  0,  0}
//        { 1, 1,  0,  0,  0}
 
    MatrixPage MatPg1;
    MatPg1.Create("Origin");
    MatrixLayer MatLy1 = MatPg1.Layers(0);
    Matrix Mat1(MatLy1);
    Mat1 = mat1;
    printf("  Original matrix is %s.\n",Mat1.GetName());
 
    MatrixPage MatPg2;
    MatPg2.Create("Origin");
    MatrixLayer MatLy2 = MatPg2.Layers(0);
    Matrix Mat2(MatLy2);
 
    int rc=Mat1.GetLowerTriangular(Mat2); //Put the lower triangular matrix of Mat1 to Mat2
    if(rc!=0) 
        printf("  Error: GetLowerTriangular failed. Error Code=%d\n",rc);
    else 
    {
        printf("  Lower triangular matrix is %s.\n",Mat2.GetName());
        printf("  Note that the NANUM in the lower triangular area is preserved,\n");
        printf("  Note that the NANUM in the upper triangular area became 0,\n");
    }
    
    
    MatrixPage MatPg3;
    MatPg3.Create("Origin");
    MatrixLayer MatLy3 = MatPg3.Layers(0);
    Matrix Mat3(MatLy3);
    
    rc=Mat1.GetLowerTriangular(Mat3,-1); //Put the lower triangular matrix of Mat1 to Mat3 from the 1th diagonal below the main diagonal
    if(rc!=0) 
        printf("  Error: GetLowerTriangular failed. Error Code=%d\n",rc);
    else 
    {
        printf("  Lower triangular matrix is %s.\n",Mat3.GetName());
        printf("  Note that the NANUM in the lower triangular area is preserved,\n");
        printf("  Note that the NANUM in the upper triangular area became 0,\n");
    }
 
}

Remark

Get a lower triangular matrix from this matrix. This matrix and the result matrix may be the same.

See Also

matrixbase::GetUpperTriangular, matrixbase::MakeIdentity, matrixbase::SetDiagonal, matrixbase::GetDiagonal

header to Include

origin.h