# Why do I get "Array indices must be positive integers or logical values" in line 17

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%prameters
L = 160
w = 1000 * 2 * pi/60
r = 60
N = 100
th0 = 0
thl = 180
dth = (thl - th0)/N
q=r/L
l = 0
%calculation
for i = 0:1:N
th = (th0 + i * dth) * pi/180;
phi = asin (q * sin(th));
dphidt = w * q * cos(th)/sqrt(1 - (q * sin(th))^2);
vD (i + l) = w * r * sin(phi + th)/cos(phi);
wBD(i + l) = -w * r * cos(th)/(L * cos(phi));
aD(i + l)= w * r * ((cos(phi) * cos(phi + th) * (w + dphidt) - sin(phi) * sin(phi + th) * dphidt)/cos(phi)^2);
alBD (i + l) = -w * q * ((-cos(phi) * sin(th) * w + sin(phi) * cos(th) *dphidt)/cos(phi)^2);
end
figure
plot ((th0:dth:thl) , wBD , (th0:dth:thl) , alBD/100 ,'lineWidth', 2);
xlabel ('\theta ({\circ})') ;
axis ([th0 thl - inf inf]);
figure
plot ( [th0:dth:thl] , vD/10 , [th0:dth:thl] , aD/1000 , 'LineWidth' , 2 );
xlabel ('\theta ({\circ})');
legend ('v_D (10^1 in/s)','a_D (10^3 in/s^2)');
axis ([tho thl - inf inf]);
N = 100
thl = 180
N = 100
clc
DGM on 21 Nov 2021
(i+l) is zero because both i and l are zero. Zero is not a valid array index.

Srijith Kasaragod on 23 Nov 2021
Hi Omar,
When for loops begins execution, loop variable 'i' is initialized to 0. Also variable 'l' is 0. Hence array index 'i+l' returns 0 which is not valid array indexing in MATLAB. Array indexing in MATLAB starts at 1.
Regards.