source("abcd.m")


########################################## 
# an example of 'answ.txt' file
#lambda= 1.064E-6 ;
#Ltot= 1 ;
#r0= 1.0E+100 ;
#w0= 25.63e-6;
#lns1.abcd=abcd_lens( 0.25 ) ;
#lns1.x= 0.37680270021479 ;
#lns2.abcd=abcd_lens( 0.1 ) ;
#lns2.x= 0.90277021575519 ;
#rf=1e100;
#wf=25.630e-6;
########################################## 
source("answ.txt")


q0=waste_r2q(w0,r0,lambda);
optics={lns1,lns2,lns3};
optics_forward=optics;

x=0:.001:Ltot;
printf("=================================\n")
q1=prop(x,q0,optics);
printf("=================================\n")
w1=q2waste(q1, lambda);
r1=q2radius(q1,lambda);

printf("=================================\n")
#q1b=prop(Ltot,q0,optics)
#wb=q2waste(q1b, lambda)
#rb=-q2radius(q1b,lambda)
#because of back propogation
rf=-rf;
q1b=waste_r2q(wf,rf,lambda);

lns1.x=Ltot-lns1.x;
lns2.x=Ltot-lns2.x;
lns3.x=Ltot-lns3.x;
optics={lns3,lns2,lns1};
q2b=prop(x,q1b,optics);
printf("=================================\n")
wb=q2waste(q2b, lambda);
rb=q2radius(q2b,lambda);
xb=Ltot-x;
#plot (x,w1, "1")
plot (x,w1, "1;forward propagation;", xb, wb, "2;backward propagation;",
      x,-w1, "1;;", xb, -wb, "2;;")
%gset term postscript;
%gset output "waist_profile.ps"
%replot
%gset term png;
%gset output "waist_profile.png"
%replot
%gset term gif;
%gset output "waist_profile.gif"
%replot

printf("=================================\n")
printf("======= final check =============\n")
printf("======= after propogatin ========\n")
printf("following are theoretical values: \n")
w0
r0
wf
rf
q0=waste_r2q(w0,r0,lambda);
optics=list(lns1,lns2,lns3);
qtf=prop(Ltot, q0, optics_forward);
printf("values below should match 'wf' and 'rf': \n")
waste = q2waste(qtf, lambda)
radius = q2radius(qtf,lambda)

pause(100)
quit()