Matrix filling with for loop

Hi everybody. so i'm an ultra beginner in matlab and i need your help to find a solution to the problem i have.

i'm trying to make a very simple calculations for solid state physics, it should be something like z = constant * x/y , to plot a surface graph of z, to evaluate the applicability limits of my experiment. x and y are identical vectors from 1 to 100 in steps of 1. In my mind, i think I need to build a matrix where the elements cosists in all the possible ratios between the single elements of x and y, in order to obtain my surface. I think i need to employ a for loop but i'm a bit stuck on the syntax. is there anyone that can help me? many thanks Francesco

[M]

Did you already read the documentation ?

If yes, what have you tried and what is your problem exactly ?

[Bruccio]

yes, i read the documentation. i can't formalize decently the loop so that the matrix is filled with the values i refer to in my question. my current code is

f = zeros (100, 100) %I create the matrix that will lateley be filled with the values x = (1: 1: 100) %create the vectors

for w = (:, x)

for s = (:, x) f (:, x) = w/s end

of course MATAB tells me that : is not a valid my skill and experience in matlab are EXTREMELY limited and i'm still trying to figure out how coding works. i've seen a lot of tutarials and read a lot of voices, still need to figure out how to translate everything into code

Answer 1

[M]

For loop documentation : https://fr.mathworks.com/help/matlab/ref/for.html?searchHighlight=for&s_tid=doc_srchtitle

f = zeros (100, 100) %I create the matrix that will lately be filled with the values

Correct, but you don't have to define your x vector to do the for loop.

If you want to loop over 100 element in step of one, you can write it like :

   for i=1:1:100  
   for i=1:100

Both solution are the same because default step is 1.

But you should start to write the program you want to use, and then convert it into Matlab language.

[Bruccio]

thanks for the advice. i don't know any coding language, i'm writing directly into MATLAB...i still don't get what is wrong with my code. it doesn't accept the colon operator. i know i can operate with both colums or row, in this case i'm basically telling him to go to fill the nth (1<=n<=100) with the result of the w/s operation, with w = nx. that should do the trick, but it doesn't work. chnanged my code to

for w = (1 : 1 : 100)

for s = (1 : 1 : 100)

f (:, x) = w/s

end

no error messages, but nothing happens to the matrix

[M]

I don't really get hat you're are trying to do

i don't know any coding language : just write it in english, like :

   Step 1 : create a matrix f of dimension (2,2)
   Step 2 : for i=[1 2 3 4]
               Compute z=1/i;
            end for
   Step 3 : Assign to the first element of f the first element of z

[Bruccio]

i want to obtain the following matrix

1 1/2 1/3 1/4 ... 1/100

2 2/2 2/3 2/4 ... 2/100

3 3/2 3/3 3/4 ... 3/100

4 4/2 4/3 4/4 ... 4/100

.

.

.

100 100/2 100/3 100/4 ... 100/100

maybe i should have written this from the beginning...sorry

[M]

Ok, it is clear now.

So, the way you initialize your matrix is ok.

   f = zeros (100, 100);

what you can do, is to loop over 100 elements, for example for each row, and set each row to the desired value. Something like :

   f=zeros(100,100);
   for i = ... % loop over 100 elements
               % i should take value 1, 2,3 ...
               % then you can access ith row of f with f(:,i)
       f(:,i) = ... % set the desired value for each row
                    % for example, your first row can be defined as 
                    % f(:,1)=[1:100]'
   end        % end of for loop
   f          % display the result

[Bruccio]

exactly. Thanks a lot man. you're my favourite person of the week.