-- File:	Crout.cdl
-- Created:	Thu Aug 22 10:57:59 1991
-- Author:	Laurent PAINNOT
--		<lpa@topsn3>
---Copyright:	 Matra Datavision 1991, 1992



class Crout from math

    	---Purpose: This class implements the Crout algorithm used to solve a 
   	--          system A*X = B where A is a symmetric matrix. It can be used to
    	--          invert a symmetric matrix.
    	--          This algorithm is similar to Gauss but is faster than Gauss.
    	--          Only the inferior triangle of A and the diagonal can be given.


uses Matrix from math, 
     Vector from math,
     OStream from Standard

raises NotDone from StdFail,
       NotSquare from math,
       DimensionError from Standard

is

    Create(A: Matrix; MinPivot: Real = 1.0e-20)
    	---Purpose: Given an input matrix A, this algorithm inverts A by the
    	--          Crout algorithm. The user can give only the inferior 
    	--          triangle for the implementation.
    	--          A can be decomposed like this:
    	--          A = L * D * T(L) where L is triangular inferior and D is 
    	--          diagonal.
    	--          If one element of A is less than MinPivot, A is
    	--          considered as singular.
    	--          Exception NotSquare is raised if A is not a square matrix.

    returns Crout
    raises NotSquare;
    
    
    IsDone(me)
    	---Purpose: Returns True if all has been correctly done.
    	---C++: inline
    returns Boolean
    is static;
    

    Solve(me; B: Vector; X: out Vector)
    	---Purpose: Given an input vector <B>, this routine returns the 
    	--          solution of the set of linear equations A . X = B.
    	--          Exception NotDone is raised if the decomposition was not
    	--          done successfully.
    	--          Exception DimensionError is raised if the range of B is
    	--          not equal to the rowrange of A.

    raises NotDone, 
    	   DimensionError
    is static;
    

    Inverse(me)
    	---Purpose: returns the inverse matrix of A. Only the inferior 
    	--          triangle is returned.
    	--          Exception NotDone is raised if NotDone.
    	---C++: inline
    	---C++: return const&
    returns Matrix
    raises NotDone
    is static;
    
    
    Invert(me; Inv: out Matrix)
    	---Purpose: returns in Inv the inverse matrix of A. Only the inferior 
    	--          triangle is returned.
    	--          Exception NotDone is raised if NotDone.
    	---C++: inline

    raises NotDone
    is static;


    Determinant(me)
    	---Purpose: Returns the value of the determinant of the previously LU
    	-- decomposed matrix A. Zero is returned if the matrix A is considered as singular.
    	-- Exceptions
    	-- StdFail_NotDone if the algorithm fails (and IsDone returns false).
    	---C++: inline    
    returns Real
    raises NotDone
    is static;


    Dump(me; o: in out OStream)
	---Purpose: Prints on the stream o information on the current state 
    	--          of the object.

    is static;



fields

InvA:  Matrix;
Done:  Boolean;
Det:   Real;

end Crout;