Why does numpy produce a runtime warning (invalid value encountered in log) when taking the log of a negative number? I noticed that if you coerce the argument to complex by adding 0j to the negative number, the expected result is produced (i.e. ln(-1) = pi*i).
I was surprised I couldn't find a discussion on this, as I would have expected others to have come across this before. Packages like Matlab handle negative numbers automatically by doing the complex conversion.
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