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  • Committer: Bazaar Package Importer
  • Author(s): Torsten Werner
  • Date: 2002-03-21 16:57:43 UTC
  • Revision ID: james.westby@ubuntu.com-20020321165743-e9mv12c1tb1plztg
Tags: upstream-2.6
Import upstream version 2.6

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macros/algebre/spanplus.sci
 
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function [x,dim,dima]=spanplus(a,b,tol)
 
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//[X,dim,dima]=spanplus(A,B,tol) computes an orthogonal basis of
 
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// a+b such that : the first dima columns of x span Range(A)
 
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// and the following (dim-dima) columns make a basis of a+b
 
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// relative to a. tol is an optional argument.
 
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// The dim first columns of x make a basis for A+B.
 
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//F.D.
 
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//!
 
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// Copyright INRIA
 
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[na,ma]=size(a);[nb,mb]=size(b);
 
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if na*ma==0 then [x,dima]=rowcomp(b);dim=dima;x=x';return;end
 
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if nb*mb==0 then [x,dima]=rowcomp(a);dim=dima;x=x';return;end
 
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[lhs,rhs]=argn(0);
 
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if rhs==2 then tol=%eps*na*nb*ma*mb;end
 
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if na<>nb then error('uncompatible dimensions!'),end
 
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[x,dima]=rowcomp(a);
 
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b=x*b;x=x'    //update b,x
 
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if dima == na then dim=dima,return,end;
 
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low=(dima+1):na;
 
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blow=b(low,:);
 
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if norm(blow,1) <= tol*norm(b,1),dim=dima,return,end
 
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[u2,r2]=rowcomp(blow);
 
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dim=dima+r2;
 
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x(:,low)=x(:,low)*u2';    //update
 
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