Matrix visualization

[Jack Poulson]

Dear all,

There is not yet any documentation, but the development branch now supports the routines "Display" and "Spy" if Qt5 was detected by CMake.

For example, the examples/matrices/Walsh driver:
https://github.com/poulson/Elemental/blob/master/examples/matrices/Walsh.cpp

produces a Walsh matrix, displays the matrix, computes its LDL^T factorization, and then displays the L and D factors (the L factor can be seen to be the Sierpinski triangle).

From a fresh checkout (assuming Qt5 is installed), one might want to run:

cd elemental
mkdir build
cd build

cmake -D ELEM_EXAMPLES=ON ..

make examples-matrices-Walsh

./bin/examples/matrices/Walsh --print false --order 8

Jack