correct comments/errors about trace; add making diagonal matrix #1469

Job	Run time
macos-latest: clang++ Release Threads	2m 36s
macos-latest: clang++ Release OneTBB	4m 14s
macos-latest: clang++ Release PaRSEC	3m 39s
ubuntu-20.04: /usr/bin/g++-9 Release Threads	1m 2s
ubuntu-20.04: /usr/bin/g++-9 Release OneTBB	1m 55s
ubuntu-20.04: /usr/bin/g++-9 Release PaRSEC	3m 27s
macos-latest: clang++ Debug Threads	2m 32s
macos-latest: clang++ Debug OneTBB	4m 39s
macos-latest: clang++ Debug PaRSEC	3m 22s
ubuntu-20.04: /usr/bin/g++-9 Debug Threads	1m 20s
ubuntu-20.04: /usr/bin/g++-9 Debug OneTBB	1m 34s
ubuntu-20.04: /usr/bin/g++-9 Debug PaRSEC	3m 26s
	33m 46s

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