Multiple matrix solve

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If A is a square or symmetric matrix use 

    CroutMatrix X = A;                // carries out LU decomposition
    Matrix AP = X.i()*P; Matrix AQ = X.i()*Q;
    LogAndSign ld = X.LogDeterminant();
rather than 
    Matrix AP = A.i()*P; Matrix AQ = A.i()*Q;
    LogAndSign ld = A.LogDeterminant();
since each operation will repeat the LU decomposition.

If A is a BandMatrix or a SymmetricBandMatrix begin with 

    BandLUMatrix X = A;               // carries out LU decomposition
A CroutMatrix or a BandLUMatrix can't be manipulated or copied. Use references as an alternative to copying. Alternatively use 
    LinearEquationSolver X = A;
This will choose the most appropiate decomposition of A. That is, the band form if A is banded; the Crout decomposition if A is square or symmetric and no decomposition if A is triangular or diagonal. If you want to use the LinearEquationSolver #include newmatap.h.