Graphs the complex logarithm. The logarithm can be defined for the complex numbers based on the most important identity of complex analysis, that z=x+iy=r*exp(i*θ)=exp(ln(r)+θi), where the rectilinear form is (x,y) and the polar form is (θ,r). Then, log(z) = log(exp(ln(r)+θi)) = ln(r)+θi. http://en.wikipedia.org/wiki/Complex_logarithm
