exchange operator apply working in low rank form and is faster #1544

Job	Run time
macos-latest: clang++ Release Threads	29m 34s
macos-latest: clang++ Release OneTBB	2m 13s
macos-latest: clang++ Release PaRSEC	4m 19s
ubuntu-20.04: /usr/bin/g++-9 Release Threads	52m 34s
ubuntu-20.04: /usr/bin/g++-9 Release OneTBB	2m 34s
ubuntu-20.04: /usr/bin/g++-9 Release PaRSEC	2m 40s
macos-latest: clang++ Debug Threads	27m 11s
macos-latest: clang++ Debug OneTBB	3m 8s
macos-latest: clang++ Debug PaRSEC	4m 53s
ubuntu-20.04: /usr/bin/g++-9 Debug Threads	53m 48s
ubuntu-20.04: /usr/bin/g++-9 Debug OneTBB	3m 24s
ubuntu-20.04: /usr/bin/g++-9 Debug PaRSEC	2m 56s
	3h 9m 14s

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