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> The Fortran standard says the result is supposed to be the principal value, which is +2i. The exact phrase is "the principal value with the real part greater than or equal to zero." In other words, there are 2 principal values. This is consistent with the DLMF (NIST) term "closed definition of the principal value": http://dlmf.nist.gov/4.2#i The link is for the natural logarithm, but the same logic should apply for SQRT, because SQRT( z ) = EXP( LOG( z ) / 2 ). Anyway, the correct answer for SQRT( CMPLX( -4, -0 )) must be (0,-2) as long as the processor can distinguish +0 and -0. Anton P.S. This wasn't an abstract example. A colleague was trying to understand why Matlab and Fortran gave the answers of opposite sign for this expression.