Product of two symmetric SMatrix objects

ROOT
1

Hello,

I am trying to use (root 6.10.07) symmetric SMatrix in my code, one of the operations being a product of 2 symmetric matrices. I expect the result to be also symmetric matrix, e.g.

using CovSMatrixD = ROOT::Math::SMatrix<double,3, 3, ROOT::Math::MatRepSym<double, 3>>;
CovSMatrixD m0,m1, mprod;
mprod = m0*m1;

mprod to be of the type CovSMatrixD, but such a code fails to compile with error quoted below. In opposite,
auto mproda = m0*m1; works w/o problem, but the mproda appears to be of the type ROOT::Math::Expr<MatrixMulOp<SMatrix<double, 3, 3, MatRepSym<double, 3> >, SMatrix<double, 3, 3, MatRepSym<double, 3> >, double, 3>, double, 3, 3, MatRepStd<double, 3, 3> >
which explains why the compilation fails.

From the SMatrix code I see that the
template <class R2> SMatrix<T,D1,D2,R>& operator*=(const SMatrix<T,D1,D2,R2>& rhs);
should do what I need, but why it is not used? Is this a bug?

In fact, the lines like

CovSMatrixD m0,m1; 
m1 *= m0;

also lead to compilation error.

Attached macro mtst.C (921 Bytes) shows the problem:

root [0] .x mtst.C+
Info in <TUnixSystem::ACLiC>: creating shared library /home/shahoian/Downloads/./mtst_C.so
In file included from input_line_11:9:
In file included from ././mtst.C:4:
In file included from /home/shahoian/alice/sw/ubuntu1604_x86-64/ROOT/v6-10-06+git_c54db1c10b-1/include/Math/SMatrix.h:734:
In file included from /home/shahoian/alice/sw/ubuntu1604_x86-64/ROOT/v6-10-06+git_c54db1c10b-1/include/Math/SMatrix.icc:53:
/home/shahoian/alice/sw/ubuntu1604_x86-64/ROOT/v6-10-06+git_c54db1c10b-1/include/Math/HelperOps.h:136:10: error: no matching conversion for functional-style cast from 'ERROR_Cannot_assign_general_to_symmetric_matrix *' to
      'ROOT::Math::CompileTimeChecker<(0 == 1) != 0>'
         STATIC_CHECK(0==1, Cannot_assign_general_to_symmetric_matrix);
         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/home/shahoian/alice/sw/ubuntu1604_x86-64/ROOT/v6-10-06+git_c54db1c10b-1/include/Math/StaticCheck.h:59:12: note: expanded from macro 'STATIC_CHECK'
   (void) (ROOT::Math::CompileTimeChecker<(expr) != 0> (&e)); }
           ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/home/shahoian/alice/sw/ubuntu1604_x86-64/ROOT/v6-10-06+git_c54db1c10b-1/include/Math/SMatrix.icc:164:28: note: in instantiation of member function 'ROOT::Math::Assign<double, 3, 3, ROOT::Math::MatrixMulOp<ROOT::Math::SMatrix<double, 3, 3,
      ROOT::Math::MatRepSym<double, 3> >, ROOT::Math::SMatrix<double, 3, 3, ROOT::Math::MatRepSym<double, 3> >, double, 3>,
      ROOT::Math::MatRepSym<double, 3>, ROOT::Math::MatRepStd<double, 3, 3> >::Evaluate' requested here
   Assign<T,D1,D2,A,R,R2>::Evaluate(*this, rhs);
                           ^
/home/shahoian/alice/sw/ubuntu1604_x86-64/ROOT/v6-10-06+git_c54db1c10b-1/include/Math/SMatrix.icc:108:4: note: in instantiation of function template specialization 'ROOT::Math::SMatrix<double, 3, 3, ROOT::Math::MatRepSym<double, 3>
      >::operator=<ROOT::Math::MatrixMulOp<ROOT::Math::SMatrix<double, 3, 3, ROOT::Math::MatRepSym<double, 3> >, ROOT::Math::SMatrix<double, 3, 3,
      ROOT::Math::MatRepSym<double, 3> >, double, 3>, ROOT::Math::MatRepStd<double, 3, 3> >' requested here
   operator=(rhs);
   ^
././mtst.C:34:22: note: in instantiation of function template specialization 'ROOT::Math::SMatrix<double, 3, 3, ROOT::Math::MatRepSym<double, 3>
      >::SMatrix<ROOT::Math::MatrixMulOp<ROOT::Math::SMatrix<double, 3, 3, ROOT::Math::MatRepSym<double, 3> >, ROOT::Math::SMatrix<double, 3, 3,
      ROOT::Math::MatRepSym<double, 3> >, double, 3>, ROOT::Math::MatRepStd<double, 3, 3> >' requested here
  CovSMatrixD mmi1 = m0*m0inv;
                     ^
/home/shahoian/alice/sw/ubuntu1604_x86-64/ROOT/v6-10-06+git_c54db1c10b-1/include/Math/StaticCheck.h:51:24: note: candidate constructor (the implicit copy constructor) not viable: no known conversion from 'ERROR_Cannot_assign_general_to_symmetric_matrix *' to
      'const ROOT::Math::CompileTimeChecker<false>' for 1st argument
     template<> struct CompileTimeChecker<false> {};
                       ^
/home/shahoian/alice/sw/ubuntu1604_x86-64/ROOT/v6-10-06+git_c54db1c10b-1/include/Math/StaticCheck.h:51:24: note: candidate constructor (the implicit move constructor) not viable: no known conversion from 'ERROR_Cannot_assign_general_to_symmetric_matrix *' to
      'ROOT::Math::CompileTimeChecker<false>' for 1st argument
     template<> struct CompileTimeChecker<false> {};
                       ^
/home/shahoian/alice/sw/ubuntu1604_x86-64/ROOT/v6-10-06+git_c54db1c10b-1/include/Math/StaticCheck.h:51:24: note: candidate constructor (the implicit default constructor) not viable: requires 0 arguments, but 1 was provided
Error in <ACLiC>: Dictionary generation failed!
2

Hi,
I’m not the author of the code but the product of two symmetric matrices is not necessarily symmetric, so at compile-time, when the types of the objects have to be decided, I guess one has to go with a more relaxed assumption.
@moneta can probably confirm (or correct me).

3

Hi @eguiraud

Thanks a lot, indeed, I have completely missed that the final matrix might be indeed asymmetric. So, my question was wrong…

Cheers
Ruben

4

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