Inserting a row into the matrix in each iterations

Hi there i like to ask how can i insert a new row/colum into the matrix with each increasing of the iterations

for i=1:n-1
    h(i)=x(i+1)-x(i);
    iter_h=iter_h+1;
    Dia_1= [1 h(i) h(i+1)]     
end

My interest is to add one coloum into Dia_1 for each iterations, for example Dia_1=[1 h(1) h(2) h(3) and so on for every new i, the h(i) will pop up here

How can i do so?

[Rik]

Dynamically growing a variable is generally a bad idea. It sounds like you simply need to do this

Dia_1=[1;h(1:i)];
%       ^ because you said you wanted to add rows, not columns

If the code you posted is the real code instead of just an example, you probably should be using diff instead.

[Mark Loui]

Ok i will use the diff but if i use diff method how can i approach with the code

[Rik]

You didn't tell me what your goal is, so you will have to read the documentation yourself.

[Mark Loui]

Hi i have read about the diff method, it seems it is decreasing the matrix increase of increasing the matrix, i have also tried your method, it just runs n times where the matrix is not increasing in coloum/row, it remains the same for all the iterations.

To change it to coloum i just

Dia_1=[1;h(i:1)]; is this right?

[Adam Danz]

I believe Rik is suggesting that your loop is doing what the diff function does.

h = diff(x);

[Rik]

That is indeed what I meant: if you want to calculate x(i+1)-x(i) for all positions of x, then you can simply do diff(x) to get the same result.

I have no clue what you are trying to achieve, so I can't give you a real solution. What do you want to do with Dia_1?

If you have trouble with Matlab basics you may consider doing the Onramp tutorial (which is provided for free by Mathworks).

Answer 1

[Juan Diego Castillo Cruz]

I understand that you want to make the variable grow every iteration. Then:

Dia_1=[]; %Create a array
for i=1:n-1
    h(i)=x(i+1)-x(i);
    iter_h=iter_h+1;
    Dia_1 = [Dia_1 h(i)] %This insert columns
end

[Adam Danz]

Yea, but it's generally a bad idea to dynamically increase variable sizes. 1) it's slow, 2) most of the time the final size of the array is known before its produced so why let the loop determine its size?

A better implementation of your answer would be,

Dia_1 = nan(1,n-1): % for a row vector
for i = 1:n-1
    . . .
    Dia_1(i) = h(i);
end

[Mark Loui]

Hi Juan Diego i have another question, yes you have answer my question to insert a new row, but if i have a specific equations i like to put inside the new coloum, how can i do so?

Your codes suggest that each new coloum will place the new h value at each iterations, my main goals was to have a h(i) as the first and then the new coloumn is 2(h(i+1)+h(i)) this is my main objective how can implement this into the code?

Do i do it as Dia_1=[Dia_1 h(i), Dia_1*(h(i+1)+h(i))]

Can i do it like this?

[Rik]

Did you already do a basic Matlab tutorial? It sounds like that would be a good time investment.

[Juan Diego Castillo Cruz]

I assume that h is a matrix then:

h = ones(m,n-1);
Dia_1 = ones(m,n)
for i=1:n-1
    h(:,i) = [i 2*i 3*i];   %For example this vector
    Dia_1(:,i+1)=h(:,i).*Dia_1(:,i);
end

This was my understanding.