# Interface RealLinearOperator

All Known Implementing Classes:
AbstractRealMatrix, Array2DRowRealMatrix, BlockRealMatrix, DiagonalMatrix, JacobiPreconditioner, OpenMapRealMatrix

public interface RealLinearOperator
This class defines a linear operator operating on real (double) vector spaces. No direct access to the coefficients of the underlying matrix is provided.

The motivation for such an interface is well stated by Barrett et al. (1994):

We restrict ourselves to iterative methods, which work by repeatedly improving an approximate solution until it is accurate enough. These methods access the coefficient matrix A of the linear system only via the matrix-vector product y = A · x (and perhaps z = AT · x). Thus the user need only supply a subroutine for computing y (and perhaps z) given x, which permits full exploitation of the sparsity or other special structure of A.
Barret et al. (1994)
R. Barrett, M. Berry, T. F. Chan, J. Demmel, J. M. Donato, J. Dongarra, V. Eijkhout, R. Pozo, C. Romine and H. Van der Vorst, Templates for the Solution of Linear Systems: Building Blocks for Iterative Methods, SIAM
• ## Method Summary

Modifier and Type
Method
Description
int
getColumnDimension()
Returns the dimension of the domain of this operator.
int
getRowDimension()
Returns the dimension of the codomain of this operator.
default boolean
isTransposable()
Returns true if this operator supports operateTranspose(RealVector).
RealVector
operate(RealVector x)
Returns the result of multiplying this by the vector x.
default RealVector
operateTranspose(RealVector x)
Returns the result of multiplying the transpose of this operator by the vector x (optional operation).
• ## Method Details

• ### getRowDimension

int getRowDimension()
Returns the dimension of the codomain of this operator.
Returns:
the number of rows of the underlying matrix
• ### getColumnDimension

int getColumnDimension()
Returns the dimension of the domain of this operator.
Returns:
the number of columns of the underlying matrix
• ### operate

Returns the result of multiplying this by the vector x.
Parameters:
x - the vector to operate on
Returns:
the product of this instance with x
Throws:
MathIllegalArgumentException - if the column dimension does not match the size of x
• ### operateTranspose

default RealVector operateTranspose(RealVector x) throws
Returns the result of multiplying the transpose of this operator by the vector x (optional operation).

The default implementation throws an UnsupportedOperationException. Users overriding this method must also override isTransposable().

Parameters:
x - the vector to operate on
Returns:
the product of the transpose of this instance with x
Throws:
MathIllegalArgumentException - if the row dimension does not match the size of x
UnsupportedOperationException - if this operation is not supported by this operator
• ### isTransposable

default boolean isTransposable()
Returns true if this operator supports operateTranspose(RealVector).

If true is returned, operateTranspose(RealVector) should not throw UnsupportedOperationException.

The default implementation returns false.

Returns:
false