When doing calculations, I sometimes run into the situation where being real and imaginary greatly affects the answer. For example, when I do integration sometimes, I end up with the result:
[numerical/symbolical answer], Assuming "a" is real, assuming Re[b]>0, etc
In extreme cases, this sometimes turns what should be 1 to 2 second calculations into being minutes long.
And if I want to find the complex conjugate of some expressiong (lets say "a*b*i"). It will come up as -i * Conjugate[ab]. But a and b are reals, so their conjugate is just the original value. Is there a way to explicitly tell Mathematica to treat certain variables as imaginary or real?