RWBandFact<T>

Module:  Linear Algebra   Group:  Factorization classes

Does not inherit

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• Synopsis
• Description
• Example
• Public Constructors
• Public Member Functions

Members

cols() condition() determinant()

factor() fail() good()

isSingular() rows() RWBandFact<T>()

RWBandFact(); solve()

#include <rw/lapack/bandfct.h>

RWBandFact<double> LU5(E);      // E is a RWBandMat<double>

A factorization is a representation of a matrix that can be used to efficiently solve systems of equations, and to compute the inverse, determinant, and condition number of a matrix. The class RWBandFact<T> encapsulates factorizations of banded matrices. Provided the matrix being factored is nonsingular, the resulting factorization can always be used to solve a system of equations.

#include <iostream>
#include <rw/lapack/bandmat.h>
#include <rw/math/mathvec.h>
#include <rw/lapack/bandfct.h>

int main()
{
   // Read in a matrix and a right-hand side and 
   // print the solution
   RWGenMat<double> A;
   RWMathVec<double> b;
   std::cin >> A >> b;
   RWBandFact<double> BF(A);
   if (BF.good()) {
     std::cout << "solution is " << solve(BF,b) << std::endl;
   } else {
     std::cout << "Could not factor A, perhaps it is singular" 
               << std::endl;
   }
     return 0;
}

RWBandFact();

Default constructor. Builds a factorization of a 0 x 0 matrix. You use the member function factor to fill in the factorization.

RWBandFact<T>(const RWBandMat<T>& A, bool ec=true);

Constructs a factorization of the matrix A. This factorization can be used to solve systems of equations, and to calculate inverses and determinants. If the parameter ec is true, you can use the function condition to obtain an estimate of the condition number of the matrix. Setting ec to false can save some computation if the condition number is not needed.

unsigned    
cols() const;

Returns the number of columns in the matrix represented by this factorization.

void  
factor(const RWGenMat<T>& A, bool void ec=true);

Factors a matrix. Calling factor replaces the current factorization with the factorization of the matrix A. This is commonly used to initialize a factorization constructed with the default (no arguments) constructor.

bool    
fail() const;
bool    
good() const;

Checks whether the factorization is successfully constructed. If good returns false or fail returns true, attempting to use the factorization to solve a system of equations results in an exception being thrown.

bool    
isSingular() const;

Tests if the matrix is singular to within machine precision. If the factorization is a positive definite type and the matrix that was factored is not actually positive definite, then isSingular may return true regardless of whether or not the matrix is actually singular.

unsigned    
rows() const;

Returns the number of rows in the matrix represented by this factorization.

T          
condition(const RWBandFact<T>& A);
rw_numeric_traits<T>::norm_type
condition(const RWGenFact<T>& A);

Calculates the reciprocal condition number of the matrix represented by this factorization. If this number is near 0, the matrix is ill-conditioned and solutions to systems of equations computed using this factorization may not be accurate. If the number is near 1, the matrix is well-conditioned. For the condition number to be computed, the norm of the matrix must be computed at the time the factorization is constructed. If you set the optional boolean parameter in the constructor or the factor member function to false, calling condition generates an exception.

T          
determinant(const RWBandFact<T>& A);

Calculates the determinant of the matrix represented by this factorization.

RWMathVec<T>          
solve(const RWBandFact<T>& A, const RWMathVec<T>& b);

Solves a system of equations. Returns the vector x, which satisfies Ax=b, where A is the matrix represented by the factorization. It is wise to call one of the member functions good or fail to make sure that the factorization was successfully constructed.

RWGenMat<T>           
solve(const RWBandFact<T>& A, const RWGenMat<T>& B);

Solves a system of equations. Returns the matrix X, which satisfies AX=B, where A is the matrix represented by the factorization. It is wise to call one of the member functions good or fail to make sure that the factorization was successfully constructed.

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