how to store the conditional loop data

sir/ madam please correct me.

ut=rand(15,1);
uy=([0.84;0.384;0.784]);
eval (['U_y','=[u_y;u_y;u_y;u_y;u_y]']);
for n=1:15
    if ut(n,1)<=U_y(n,1)
        ut(n,1)=ut(n,1);
    else
        ut(n,1)=0;
    end
    utt(:,1)=ut(n,1);    %% i want to store the ut as a utt in a column
end

[Jan]

Avoid cluttering unneeded parentheses:

uy=([0.84;0.384;0.784]);
%  ^                  ^   not useful

Do not use eval() in general, most of all if it can be replaced directly:

% eval (['U_y','=[u_y;u_y;u_y;u_y;u_y]']);   Nope
U_y = [u_y; u_y; u_y; u_y; u_y];

% Or more clearly:
U_y = repmat(uy, 5, 1);

It is not useful to write code, which does not do anything:

 ut(n,1)=ut(n,1);   % ??? Why?

[Chaudhary P Patel]

@Jan @Star Strider

ut(n,1)=ut(n,1)

because i want that specific element of ut which satisfy the condition and rest is zero after that i want to store it as utt.

[Star Strider]

My code tests each element of ‘ut’ against ‘U_y’ and sets it to zero if the condition is satisfied.

What result do you want?

[Jan]

@Chaudhary P Patel: The line ut(n,1)=ut(n,1) replaced the n.th element of the vector ut by the n.th element of the vector ut. This is a waste of time only.

An option to avoid this (see others in the already provided answers):

for n = 1:15
    if ut(n) <= U_y(n)
        utt(n) = ut(n);
    else
        utt(n) = 0;
    end
end

Or with a proper pre-allocation, to avoid the time-consuming growing of arrays:

utt = zero(15, 1);  % The default value is 0 now
for n = 1:15
    if ut(n) <= U_y(n)
        utt(n) = ut(n);
    end
end

Answer 1

[Star Strider]

If I understand the code correctly, it can be simply stated as:

ut=rand(15,1);
u_y=([0.84;0.384;0.784]);
U_y = [u_y;u_y;u_y;u_y;u_y];                            % Create Column Vector
utt = ut;                                               % Copy 'ut' to 'utt'
utt(ut>U_y) = 0                                         % Set Appropriate Elements To Zero

utt = 15×1

0 0 0.6317 0.7311 0.1069 0.5889 0.5515 0 0.2595 0.3677

No loops!

.

Answer 2

[Jan]

Your cleaned code:

ut  = rand(15, 1);
uy  = [0.84; 0.384; 0.784];
U_y = repmat(uy, 5, 1);
for n = 1:15
    if ut(n) > U_y(n)
        ut(n) = 0;
    end
    utt(n) = ut(n);
    %   ^ insert an index here
end

Remember, that X(k,1) can be written as X(k), which looks a little bit cleaner.

Instead of the loop, you can write:

utt = ut .* (ut <= U_y);

The expression in the parentheses is a vector of 1s and 0s and the elementwise multiplication set the wanted elements to 0.