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Subscript indices must either be real positive integers or logicals.

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nathan Short
nathan Short on 17 Sep 2019
Commented: nathan Short on 17 Sep 2019
Why do i get " Subscript indices must either be real positive integers or logicals." when i run my code and how can i fix it
%% problem parameters
P = 0.5*9.81; % [load N]
L = 0.5; % [Length M]
E = 69*10^6;
I = ((0.0032^3)*(0.0088))/12;
%%
x = (0:0.025:L);
v = zeros(length(x));
for i = 0.025:length(a)
a = 1/(E*I);
b = 1/12;
c = 1/16;
v(i) = a*((b*P*(i^3))-(1*c*P*(L^2)));
end

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Answers (2)

KALYAN ACHARJYA
KALYAN ACHARJYA on 17 Sep 2019
Edited: KALYAN ACHARJYA on 17 Sep 2019
The error is
v(i)
%..^
In Matlab indexing, the i value must be positive interger, like 1,2,3,,,,
v(1)>> Allow
v(0)>> Not Allow
v(0.25)>> Not Allow
v(-3)>> Not Allow
v(7)>> Allow
Hope you get the sufficients hints. In your case i starts from 0.25, hence v(0.25) Not allowed.
% Define a
% ????
%% problem parameters
P = 0.5*9.81; % [load N]
L = 0.5; % [Length M]
E = 69*10^6;
I = ((0.0032^3)*(0.0088))/12;
%%
x = (0:0.025:L);
v = zeros(length(x));
i=0.025:length(a)
for j =1:length(i)
a = 1/(E*I);
b = 1/12;
c = 1/16;
v(j)= a*((b*P*(i(j)^3))-(1*c*P*(L^2)));
end
Without Loop:
% Define a
% ????
%% problem parameters
P = 0.5*9.81; % [load N]
L = 0.5; % [Length M]
E = 69*10^6;
I = ((0.0032^3)*(0.0088))/12;
%%
x = (0:0.025:L);
v = zeros(length(x));
i=0.025:length(a)
a=1/(E*I);
b=1/12;
c=1/16;
v=a*((b*P.*(i.^3))-(1*c*P*(L^2)));
Any issue let me know?

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KALYAN ACHARJYA
KALYAN ACHARJYA on 17 Sep 2019
If a=20,
the what does the following means
i = 0.025:length(a)
it return i as a single element
i=0.025
Are you sure? No Need of loop.The v becomes
v =
-46.2192
If no, What exactly you are trying to do?
nathan Short
nathan Short on 17 Sep 2019
i want to return v as an array for each input of i (0;0.025;0.5). then plot the values against each other as it should display a deflection curve

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