clear all; close all;

L=10;
x=linspace(-L,L,100);
y=x;

[X,Y]=meshgrid(x,y);
m=1; % number of spirals
u=tanh(sqrt(X.^2+Y.^2)).*cos(m*angle(X+i*Y)-(sqrt(X.^2+Y.^2)));

subplot(1,2,1)
surfl(x,y,u),
shading interp
colormap(gray)
hold on
surfl(x,y,u+4), shading interp, view(-20,8)
surfl(x,y,u+8), shading interp
surfl(x,y,u+12), shading interp
surfl(x,y,u+16), shading interp
set(gca,'Zlim',[-1 17], ...
    'Ztick',[-1 0 1 3 4 5 7 8 9 11 12 13 15 16 17], ...
    'Zticklabel',{'-1','0','1','-1','0','1',...
    '-1','0','1','-1','0','1','-1','0','1'})

text(25,25,-4,'t=0')
text(25,25,0,'t=2')
text(25,25,4,'t=4')
text(25,25,8,'t=6')
text(25,25,12,'t=8')

subplot(1,2,2)
surfl(x,y,u), 
shading interp
colormap(gray)
hold on
surfl(x,y,u+4), shading interp
surfl(x,y,u+8), shading interp
surfl(x,y,u+12), shading interp
surfl(x,y,u+16), shading interp
view(-20,8)
set(gca,'Zlim',[-1 17], ...
    'Ztick',[-1 0 1 3 4 5 7 8 9 11 12 13 15 16 17], ...
    'Zticklabel',{'-1','0','1','-1','0','1',...
    '-1','0','1','-1','0','1','-1','0','1'})