Subscript indices must either be real positive integers or logicals.

Asked by nathan Short

nathan Short (view profile)

on 17 Sep 2019
Latest activity Commented on by nathan Short

nathan Short (view profile)

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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Answer by KALYAN ACHARJYA

KALYAN ACHARJYA (view profile)

on 17 Sep 2019
Edited by KALYAN ACHARJYA

KALYAN ACHARJYA (view profile)

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?

nathan Short

nathan Short (view profile)

on 17 Sep 2019
i think it would be 20?? would a = 0.5/0.025
KALYAN ACHARJYA

KALYAN ACHARJYA (view profile)

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 (view profile)

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