- Added problem size constructor to decompositions that did not have one. It preallocates member data structures.

- Updated unit tests to check above constructor.
- In the compute() method of decompositions: Made temporary matrices/vectors class members to avoid heap allocations during compute() (when dynamic matrices are used, of course).

These  changes can speed up decomposition computation time when a solver instance is used to solve multiple same-sized problems. An added benefit is that the compute() method can now be invoked in contexts were heap allocations are forbidden, such as in real-time control loops.

CAVEAT: Not all of the decompositions in the Eigenvalues module have a heap-allocation-free compute() method. A future patch may address this issue, but some required API changes need to be incorporated first.

test/schur_complex.cpp

@@ -64,4 +64,7 @@ void test_schur_complex()
   CALL_SUBTEST_2(( schur<MatrixXcf>(ei_random<int>(1,50)) ));
   CALL_SUBTEST_3(( schur<Matrix<std::complex<float>, 1, 1> >() ));
   CALL_SUBTEST_4(( schur<Matrix<float, 3, 3, Eigen::RowMajor> >() ));
+
+  // Test problem size constructors
+  CALL_SUBTEST_5(ComplexSchur<MatrixXf>(10));
 }