Fix morris constant

For some reason, a bunch of commits are included which are already part of jdherman:master. The only relevant commit is f0fa5e2.

The use case for the fix is like so: In my application, inputs to the morris method may change dynamically. Sometimes the range of variation is zero (ie., the lower and upper range of the variable is the same). In this case, the morris analyze function fails with the linalg approach.