# lftdata

Decompose uncertain objects into fixed certain and normalized uncertain parts

## Syntax

[M,Delta] = lftdata(A); [M,Delta] = lftdata(A,List); [M,Delta,Blkstruct] = lftdata(A); [M,Delta,Blkstruct,Normunc] = lftdata(A);

## Description

`lftdata `

decomposes an uncertain object into a
fixed certain part and a normalized uncertain part. `lftdata`

can also
partially decompose an uncertain object into an uncertain part and a normalized uncertain
part. Uncertain objects (`umat`

, `ufrd`

, `uss`

)
are represented as certain (i.e., not-uncertain) objects in feedback with block-diagonal
concatenations of uncertain elements.

`[M,Delta] = lftdata(A)`

separates the uncertain
object `A`

into a certain object `M`

and a normalized
uncertain matrix `Delta`

such that `A`

is equal to
`lft(Delta,M)`

, as shown below.

If `A`

is a `umat`

, then `M`

will be
`double`

; if `A`

is a `uss`

, then
`M`

will be `ss`

; if `A`

is a
`ufrd`

, then `M`

will be `frd`

. In all
cases, `Delta`

is a `umat`

.

`[M,Delta] = lftdata(A,List)`

separates the
uncertain object `A`

into an uncertain object `M`

, in
feedback with a normalized uncertain matrix `Delta`

. `List`

is a cell (or char) array of names of uncertain elements of `A`

that make up
`Delta`

. All other uncertainty in `A`

remains in
`M`

.

`lftdata(A,fieldnames(A.Uncertainty))`

is the same as
`lftdata(A)`

.

`[M,DELTA,BLKSTRUCT] = lftdata(A)`

returns an
*N*-by-1 structure array `BLKSTRUCT`

, where
`BLKSTRUCT(i)`

describes the `i`

-th normalized uncertain
element. This uncertainty description can be passed directly to the low-level structured
singular value analysis function `mussv`

.

`[M,DELTA,BLKSTRUCT,NORMUNC] = lftdata(A)`

returns
the cell array `NORMUNC`

of normalized uncertain elements. Each normalized
element has `'Normalized'`

appended to its original name to avoid confusion.
Note that `lft(blkdiag(NORMUNC{:}),M)`

is equivalent to `A`

.
The normalizations for each type of uncertain element are described in Decomposing Uncertain Objects.

## Examples

## Version History

**Introduced before R2006a**