balanc

Scilab Function
Last update : 25/04/2007

balanc - matrix or pencil balancing

### Calling Sequence

  `[Ab,X]=balanc(A)`
  `[Eb,Ab,X,Y]=balanc(E,A)`

### Parameters

- `A:` a real square matrix
- `X:` a real square invertible matrix
- `E:` a real square matrix (same dimension as `A` )
- `Y:` a real square invertible matrix.

### Description

Balance a square matrix to improve its condition number.

`[Ab,X] = balanc(A)` finds a similarity transformation `X` such that

`Ab = inv(X)*A*X` has approximately equal row and column norms.

For matrix pencils,balancing is done for improving the generalized eigenvalue problem.

`[Eb,Ab,X,Y] = balanc(E,A)` returns left and right transformations `X` and `Y` such that `Eb=inv(X)*E*Y, Ab=inv(X)*A*Y`

### Remark

Balancing is made in the functions `bdiag` and `spec` .

### Examples

    A=[1/2^10,1/2^10;2^10,2^10];
    [Ab,X]=balanc(A);
    norm(A(1,:))/norm(A(2,:))
    norm(Ab(1,:))/norm(Ab(2,:))

### See Also

`bdiag` , `spec` , `schur` ,