import graph3; import palette; size(12cm,IgnoreAspect); currentprojection=orthographic(1,-2,1); real f(pair z) {return abs(cos(z));} real Arg(triple v) { return degrees(cos((v.x,v.y)),warn=false); } surface s=surface(f,(-pi,-2),(pi,2),20,Spline); s.colors(palette(s.map(Arg),Wheel())); draw(s); real xmin=point((-1,-1,-1)).x; real xmax=point((1,1,1)).x; draw((xmin,0,0)--(xmax,0,0),dashed); xaxis3("$\mathop{\rm Re} z$",Bounds,InTicks); yaxis3("$\mathop{\rm Im} z$",Bounds,InTicks(beginlabel=false)); zaxis3("$|\cos(z)|$",Bounds,InTicks);