Update pvl_singlediode.m (#23)

* Update pvl_singlediode.m

Added iteration limit on while loop. This can be infinite if inputs are unreasonable (see comments on pvl_perez). It's good form to let user know source of error.

* Update pvl_singlediode.m

50 iterations seems fine. My current data ran fine with this limit. Thanks,

Author: joallen6

pvl_singlediode.m

@@ -338,13 +338,19 @@
 p = (A+B)./2;
 err = g(p,Iph,Io,a,Rs,Rsh);  % value of dP/dV at initial guess p
 
+iterCount = 0;
 while max(abs(B-A))>1e-6   % set precision of estimate of Imp to 1e-6 (A)
     gA=g(A,Iph,Io,a,Rs,Rsh); % value of dP/dV at left endpoint
     u=(gA.*err)<0;
     B(u)=p(u);
     A(~u)=p(~u);
     p=(A+B)/2;
     err = g(p,Iph,Io,a,Rs,Rsh);
+    
+    iterCount = iterCount + 1;
+    if iterCount > 50
+        error('Convergence failed in calc_Imp_bisect');
+    end
 end;
 Imp = p;
 
@@ -373,4 +379,4 @@
 z = z(:);
 Vmp=(Iph+Io-Imp).*Rsh - Imp.*Rs - a.*z;  % Compute V from Imp and W(phi)
 Pmp = Vmp.*Imp;
-end
+end