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

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Omar Ahmad AL Bloushi
回答： Srijith Kasaragod 2021-11-23
%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})') ;
legend ('\omega_{BD} (rad/s)','\alpha_{BD} (10^2 rad/s^2');
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

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回答（1 个）

Srijith Kasaragod
Srijith Kasaragod 2021-11-23
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.

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