# how to make if statement repeat only once ?

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tomer polsky on 16 May 2018
Commented: Guillaume on 22 May 2018
hello I am currently doing a project with matlab and simulink.
In my project I am taking current samples from matlab function and making is statment for a switch .
the problem is that my statment is working all the time , meaning that for exmaple my switch is on "1" and it is switching to "0" I want it to stay like this and not creak the statement again how is it possible ?
function [final_resolt]=relay_condition(u)
format long;
i_diff_1=u(1)-u(4);
i_diff_2=u(2)-u(5);
i_diff_3=u(3)-u(6);
ind_1=u(1)*u(4);
ind_2=u(2)*u(5);
ind_3=u(3)*u(6);
I_diff_1=0;
I_diff_2=0;
I_diff_3=0;
IND_1=1;
IND_2=1;
IND_3=1;
m=20;
I_min=1000;
for i=1:1:m
I_diff_1=(I_diff_1+i_diff_1^2);
I_diff_2=(I_diff_2+i_diff_2^2);
I_diff_3=(I_diff_3+i_diff_3^2);
IND_1=(IND_1*ind_1)/1;
IND_2=(IND_2*ind_2)/1;
IND_3=(IND_3*ind_3)/1;
end
I_diff_1=(I_diff_1/m)^0.5;
I_diff_2=(I_diff_2/m)^0.5;
I_diff_3=(I_diff_3/m)^0.5;
IND_1=IND_1/m;
IND_2=IND_2/m;
IND_3=IND_3/m;
if (I_diff_3>I_min )
final_resolt=0;
else
final_resolt=1;
end
end

Geoff Hayes on 17 May 2018
tomer - please clarify what you are attempting to do as it isn't clear (to me) what the switch is. Is the problem with the if block? Do you only want to evaluate it once?
Stephen Cobeldick on 17 May 2018
Ye this exactly what I want to do . u are currents from simulink and the final resolt is the switch . I want it to change only when time , when it changes to zero stay in this condition.
Guillaume on 22 May 2018
Since the if statement is outside of any loop, it will execute only once. Hence it's not clear what the problem is.

Aakash Deep on 22 May 2018
Hey,
From your question, I understand that you have a if condition inside a loop which you need to execute only once for a particular condition. In order to do this you can use a flag variable. Let's see this with an example, let's suppose you have an array with values 0 and 1. You have to subtract value x only on the first zero in the array.
arr = [1,1,1,0,0,1,0,0];
flag = 0;
for i = 1:len(arr)
if( flag == 0 && arr(i) == 0 )
arr(i)= arr(i) x;
flag = 1; % important part
end
% loop_continue
end
Hope this helps
Thanks,
Aakash Deep