added comments and variables name are more readable now

Ignore-this: 41c15ffd065ac70f4508aa9a3f4803ce

darcs-hash:20110412212909-067c0-a9a6d4ffa182651939b7aeae5405fbd2600c567a

1 files changed, 27 insertions, 18 deletions

diff --git a/abcd.m b/abcd.m
index 11cbe57..8404314 100644
--- a/abcd.m
+++ b/abcd.m
@@ -10,27 +10,36 @@ function qnew=q_afteer_element(q_old,abcd)
 	qnew=(q_old*abcd(1,1)+abcd(1,2))/(q_old*abcd(2,1)+abcd(2,2));
 endfunction
 
-function q = prop(x_final, q_in, elements)
-	q(size(x_final,2))=0;
-	for i=1:size(x_final,2)
-		x_final_i=x_final(i);
-		xend=0;
-		q_end=q_in;
-		for k=1:size(elements,2) 
-			el=nth(elements,k);
-			if ( el.x <= x_final_i)
-				abcd=abcd_free_space(el.x-xend);
-				q_end=q_afteer_element(q_end,abcd);
-				q_end=q_afteer_element(q_end,el.abcd);
-				xend=el.x;
+function q = prop(x_pos, q_in, elements)
+% calculate the 'q' parameter of the Gaussian beam propagating through optical
+% 'elements' array along 'x' axis at points 'x_pos'
+%  takes the gaussian beam with initial q_in parameter at x_pos(1)
+
+	Np=length(x_pos); % number of 'x' points
+	Nel=length(elements); 
+	q=0*x_pos; % q vector initialization
+	q(1)=q_in;
+	q_last_calc=q_in;
+	x_last_calc=x_pos(1); % the furthest calculated point
+	for i=2:Np
+		x_pos_i=x_pos(i);
+		for k=1:length(elements) 
+			% iterates through optical elements to make sure 
+			% we take them in account for the beam propagation
+			el=elements{k};
+			if ( (x_last_calc < el.x) && (el.x <= x_pos_i) )
+				abcd=abcd_free_space(el.x-x_last_calc);
+				q_last_calc=q_afteer_element(q_last_calc,abcd);
+				q_last_calc=q_afteer_element(q_last_calc,el.abcd);
+				x_last_calc=el.x;
 			endif
 		endfor
-		if (x_final_i > xend);
-			abcd=abcd_free_space(x_final_i-xend);
-			q_end=q_afteer_element(q_end,abcd);
-			xend=x_final_i;
+		if (x_pos_i > x_last_calc);
+			abcd=abcd_free_space(x_pos_i-x_last_calc);
+			q_last_calc=q_afteer_element(q_last_calc,abcd);
+			x_last_calc=x_pos_i;
 		endif
-		q(i)=q_end;
+		q(i)=q_last_calc;
 	endfor
 endfunction