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When I try the following commands:

assume(dr<1) // assume dr less than 1
evalc(sqrt(dr-1)) // yields complex solution as expected
evalc(sqrt(dr^2-1)) // why is this not complex?

is there a way to make the result of evalc(sqrt(dr^2-1)) come out complex?

Thank you for a great program. I have tried many and prefer this.

Matt

Because dr<1 does not imply dr^2<1, you should assume(dr>0 && dr<1)

OOps. Didn't think that one through.