Gnuplot's standard 2D and 3D plot styles can plot only real values; if you need to plot a complex-valued function f(x) with non-zero imaginary components you must choose between plotting real(f(x)) or abs(f(x)). For examples of representing complex values using color, see the http://www.gnuplot.info/demo/complex_trig.htmlcomplex trigonometric function demos (complex_trig.dem)