ops: epetra: revise rank-1 update

[mzuzek]

Contents:

• [x] revised overload constraints
• [x] added extent check
• [x] added explicit type casting for coefficients
• [x] fixed NaN injection through zero coefficients and added relevant unit test

refs #448

[mzuzek]

@fnrizzi

Here in Epetra all coefficients have the same scalar_t type. Would you prefer to allow different coefficient types a_Type, b_Type, etc. like in Eigen ?

[mzuzek]

@fnrizzi

Here in Epetra all vectors have the same T type. Would you prefer to allow different vector types T1, T2, etc. like in Eigen ?

[fnrizzi]

@fnrizzi

Here in Epetra all coefficients have the same scalar_t type. Would you prefer to allow different coefficient types a_Type, b_Type, etc. like in Eigen ?

yes please!

[fnrizzi]

yes, we should have separate types T1, T2, etc

[mzuzek]

Hi @fnrizzi, I've added different coef/vector types, as we discussed, expanded unit tests to cover all execution paths and rebased on develop.

[mzuzek]

thanks @mzuzek for your review and comments!