I'm debating whether to use C++ or Python for a largely math-based program. 
Both have great math libraries, but which language is generally faster for complex math?
I sincerely doubt that Google and Stanford don't know C++.  
"Generally faster" is more than just language.  Algorithms can make or break a solution, regardless of what language it's written in.  A poor choice written in C++ and be beaten by Java or Python if either makes a better algorithm choice.
For example, an in-memory, single CPU linear algebra library will have its doors blown in by a parallelized version done properly.
An implicit algorithm may actually be slower than an explicit one, despite time step stability restrictions, because the latter doesn't have to invert a matrix.   This is often true for hyperbolic partial differential equations.
You shouldn't care about "generally faster".  You ought to look deeply into the problem you're trying to solve and the algorithms used to solve it.  You'll do better that way than a blind language choice.
C++ or Python for an Extensive Math Program?