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Subscript indices must either be real positive integers or logicals.

Asked by nathan Short on 17 Sep 2019
Latest activity Commented on by 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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2 Answers

Answer by KALYAN ACHARJYA on 17 Sep 2019
Edited by 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?

  5 Comments

i think it would be 20?? would a = 0.5/0.025
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?
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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Answer by Image Analyst
on 17 Sep 2019

The FAQ explains it pretty well: Click here for the FAQ on that error

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