Given a symmetric matrix S and a dense matrix D, what would be the most efficient way to construct the matrix M=D^T S D (which will again be symmetric) using uBLAS.  The former query applies equally to any symmetric matrix manipulations which involve non-symmetric matrices and where the resulting matrix is symmetric.

Of the three standard techniques that come to mind:
1) direct element manipulations, and
2)
matrix<double> matrixD(n,n);
symmetric_matrix<double,lower> matrixS(n,n);
...
symmetric_matrix<double,lower> matrixM(prod(trans(matrixD),prod(matrixS,matrixD)));

3) the axpy_prod equivalent of 2) involving a temporary matrix
matrix<double> matrixTmp(prod(matrixS,matrixD));
symmetric_matrix<double,lower> matrixM(prod(trans(matrixD),matrixTmp));

which would the group recommend?  Any advice from experienced group members would be greatly appreciated.

Kind regards,
Andrew
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