[eigen] Eigen >= 3.3 and odeint

[Dale Lukas Peterson <hazelnusse@xxxxxxxxx>]

Hello,
 Using Eigen::Matrix for the state_type in odeint worked until a change in Eigen 3.3. Issue #194 [0] tracks the issue, including a recently merged patch [1] by one of the odeint maintainers to fix the issue.

The patch [1] depends on the internal namespace of Eigen. Is there any guidance from an Eigen expert on how this patch might be changed to work without depending on Eigen::internal?

Sincerely,
Luke

[0] https://github.com/headmyshoulder/odeint-v2/issues/194
[1] https://github.com/headmyshoulder/odeint-v2/pull/237