# Two different ways of using iterations

3 views (last 30 days)
Michael Peyron on 29 Jun 2020
Commented: Michael Peyron on 29 Jun 2020
I have decided to do some repetition in Matlab during this summer so I'm doing a lot of assignments again that I have already finished a couple of months ago. Though, I stumble upon a certain assignment and my solution would be:
v_stor=[];
v_liten=[];
v_mellan=[];
for i=1:length(V)
if V(i)>=10
v_stor = v_stor + V(i);
elseif V(i)<=-10
v_liten = v_liten + V(i);
else
v_mellan = v_mellan + V(i);
end
end
v_stor
v_mellan
v_liten
I think it's pretty straightfoward what I want my code to do. This gave me empty vectors and I was confused why, so I checked my earlier solution:
t = 0;
v_stor = [];
v_mellan = [];
v_liten = [];
for i= 1:length(V)
if V(t+1)>= 10
v_stor=[v_stor V(t+1)];
elseif V(t+1)<=-10
v_liten = [v_liten V(t+1)];
else
v_mellan=[v_mellan V(t+1)];
end
t=t+1;
end
v_stor
v_mellan
v_liten
So my question is, why is my second solution wrong and how come, in my earlier solution, that I used V(t+1)? It looks the same to me.
Edit: Vector V is of size 1000x1

dipak nigam on 29 Jun 2020
v_stor=[];
v_liten=[];
v_mellan=[];
for i=1:length(V)
if V(i)>=10
v_stor = [v_stor V(i)];
elseif V(i)<=-10
v_liten = [v_liten V(i)];
else
v_mellan = [v_mellan V(i)];
end
end
v_stor
v_mellan
v_liten
You were trying to add values to a vector by using '+' operator. You need to change your code like above to get the desired result.

#### 1 Comment

Michael Peyron on 29 Jun 2020
Yes, I was able to find it too.
Thanks anyway!

KSSV on 29 Jun 2020
Edited: KSSV on 29 Jun 2020
In the first case, you are not saving the result. Check the below.
v_stor=zeros(1,length(V));
v_liten=zeros(1,length(V));
v_mellan=zeros(1,length(V));
for i=1:length(V)
if V(i)>=10
v_stor(i) = V(i);
elseif V(i)<=-10
v_liten(i) = V(i);
else
v_mellan(i) = V(i);
end
end
v_stor
v_mellan
v_liten

Michael Peyron on 29 Jun 2020
I did not know this way of extracting the values existed. Thanks for telling. They only taught us how to do it with for loops.
KSSV on 29 Jun 2020
The basic building block is a loop. But in MATLAB you can avoid loop most of the times....remember the full form of MATLAB.
Michael Peyron on 29 Jun 2020