Array indices must be positive integers or logical values. This error is coming at line:while C(counter)> C(j) && abs(f)>.00001. Please help me out.

Thanks for replying sir. Can u tell me why my loop is not working. Output is showing only the initial values i assigned. Here is the full programme: D=800; d=[1 600 09 0.02 300 500; 2 500 10 0.04 100 400; 3 400 06 0.08 050 200]; g=1; P1=400; P2=300; P3=100; P=[P1;P2;P3]; del_C1=.04*P1-.16*P3+2; del_C2=.08*P2-.16*P3+4; counter=1; C=15900; j=counter; while C(counter)> C(j) && abs(f)>.00001 if sum(del_C1,del_C2)<0 && del_C1>del_C2 P1=P1+1; P2=P2; P3=P3-1; P=[P1;P2;P3]; f=D-sum(P); C=d(:,2)+d(:,3).*P+d(:,4).*P.*P; counter=counter+1; j=counter; elseif sum(del_C1,del_C2)<0 && del_C1<del_C2 P1=P1; P2=P2+1; P3=P3-1; P=[P1;P2;P3]; f=D-sum(P); C=d(:,2)+d(:,3).*P+d(:,4).*P.*P; counter=counter+1; j=counter; elseif sum(del_C1,del_C2)>0 && del_C1>del_C2 P1=P1-1; P2=P2; P3=P3+1; P=[P1;P2;P3]; f=D-sum(P); C=d(:,2)+d(:,3).*P+d(:,4).*P.*P; counter=counter+1; j=counter; elseif sum(del_C1,del_C2)>0 && del_C1<del_C2 P1=P1-1; P2=P2; P3=P3+1; P=[P1;P2;P3]; f=D-sum(P); C=d(:,2)+d(:,3).*P+d(:,4).*P.*P; counter=counter+1; j=counter; end end display(P,'Generated Power in MW') display(C,'Total Cost in $') display(counter,'Iterations numbers')