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# gschur

generalized Schur form. This function is obsolete.

### Calling Sequence

```[As,Es]=gschur(A,E)
[As,Es,Q,Z]=gschur(A,E)
[As,Es,Z,dim] = gschur(A,E,flag)
[As,Es,Z,dim]= gschur(A,E,extern)```

### Description

This function is obsolete and is now included in the `schur` function. In most cases the `gschur` function will still work as before, but it will be removed in the future release.

The first three syntaxes can be replaced by

```[As,Es]=schur(A,E)
[As,Es,Q,Z]=schur(A,E);Q=Q' //NOTE THE TRANPOSITION HERE
[As,Es,Z,dim] = schur(A,E,flag)```

The last syntax requires little more adaptations:

if

extern is a scilab function the new calling sequence should be `[As,Es,Z,dim]= schur(A,E,Nextern)` with Nextern defined as follow:

```function t=Nextern(R)
if R(2)==0 then
t=extern([1,R(1),R(3)])==1
else
c=(R(1)+%i*R(2))/R(3)
t=extern([2,real(c+c'),real(c*c')])==1
end
endfunction```
if

extern is the name of an external function coded in Fortran or C the new calling sequence should be `[As,Es,Z,dim]= schur(A,E,'nextern')` with nextern defined as follow:

```logical function nextern(ar, ai, beta)
double precision ar,ai,beta
integer r,extern
if (ai.eq.0.0d0) then
r=extern(1,ar,beta,0.0d0,0.0d0)
else
r=extern(2,0.0d0,0.0d0,2.0d0*ar,ar*ar+ai*ai)
endif
nextern=r.eq.1
end```
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