BDCSVD: Compute SVD of combined problem directly.
First step at implementing final stage in BDCSVD algorithm.
Uses bisection method to solve nonlinear equation.
Still lots of room for optimization.

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extra : transplant_source : %7F%89%E0%A5%9Ft%04%2B%B0%CA0%2BE%E9%8AHva%A6F
Allows EIGEN_STACK_ALLOCATION_LIMIT to be 0 for no limit
Add explanations of the logic behind the matrix-vector products