Save the values of a function in a for loop

I need to record the y-values of a line from x=a to x=b.

Each loop, the slope of the line will change so there will be a different set of x and y's for each loop

How can I record the y-values from the function for each loop? The above fix doesn't work if a function is inside of it. This is my code and gives me an error once it trys to record y(i):

function for_test
x = 0:1:10;
y = ones(size(x)) ;

for i=1:10
y(i) = x+rand;

y             % use y(i) so that it is written as a vector
end
end
    

[Mohammad Sami]

The problem is this line

y(i) = x+rand;

The variable x is length 11

x+rand; % this would generate an output of length 11

However you are trying to assign it to a single value of y

y(i) % this is lenght 1

Therefore you are getting an error in assignment.

[Austin Hernandez]

That is the exact error message I am getting but my question was how do I store each y values for each through each loop? I think I found a workaround, and that is to put the data into a cell array with {i}. Is that the proper fix or is there another way?

Answer 1

[Mrutyunjaya Hiremath]

Hell Austin Hernandez,

you are correct. but Option01 is good.

Option 01:

function for_test
x = 0:1:10;
y = zeros(size(x)) ;
for i=1:10
    y(i,:) = x+rand;
    y             % use y(i) so that it is written as a vector
end
end

Option 02:

function for_test
x = 0:1:10;
y = {}; %ones(size(x)) ;
for i=1:10
    y{i} = x+rand;
    y             % use y(i) so that it is written as a vector
end
end

[Austin Hernandez]

Thank you!! This is a good fix. Now... the next step after that, I need to plot a graph based upon the answers given (there's a prompt window before this).

In my for loop, I have an if, elseif, and else statement, which gives 3 very different values. Should I try to put all these into 1 cell array? How can I access the data of each array and then plot it?

Or, if I do step 1 and construct a matrix for each of the 3 options. So if it were like:

h = 0:1:10
y = zeros(size(h));
v = zeros(size(h));
o = zeros(size(h));
prompts = {'enter 1'};
dlg = 'title';
c = 0;
m = 0;
u = 0;
hold on
for i=1:5
    A = inputdlg(prompts, dlg);
    Aa = str2double(A);
    x = Aa(1);
    if x == 1
        y(i,:) = 1000*h;
        m = m + 1;
        plot(h,y(i,:));
    elseif x == 0
        v(i,:) = h+1;
        u = u + 1;    
        plot(h,v(i,:));
    else 
        o(i,:) = -h*5;
        c = c + 1; 
        plot(h,o(i,:));
    end
end
end

When I used Option 1, this method will generate a new row in the matrix of each output. So if I'm on loop 5, and the if statement is triggered, and I triggered the same statement in the very first loop, then I'll get a matrix like:

v =

     1     2     3     4     5     6     7     8     9    10    11
     0     0     0     0     0     0     0     0     0     0     0
     0     0     0     0     0     0     0     0     0     0     0
     0     0     0     0     0     0     0     0     0     0     0
     1     2     3     4     5     6     7     8     9    10    11

How can I tell matlab that I want to access the rows that have nonzero elements? And then sort them from high to low (if the rows had different values)?

[Mrutyunjaya Hiremath]

@ Austin

you are a fast learner. This can be fixed.

But please do one thing.

When you have a new bug to fix.

Then accept previous one and raise a new question.

This will help all 3 of us, myself, you and others.

Because search is always and mostly based on subject title.

[Mrutyunjaya Hiremath]

Hello Austin,

Answer is in your problem only....

h = 0:1:10
y = zeros(size(h));
v = zeros(size(h));
o = zeros(size(h));
prompts = {'enter 1'};
dlg = 'title';
c = 0;
m = 0;
u = 0;
hold on
for i=1:5
    A = inputdlg(prompts, dlg);
    Aa = str2double(A);
    x = Aa(1);
    if x == 1
        y(m,:) = 1000*h;
        m = m + 1;
        plot(h,y(m,:));
    elseif x == 0
        v(u,:) = h+1;
        u = u + 1;    
        plot(h,v(u,:));
    else 
        o(c,:) = -h*5;
        c = c + 1; 
        plot(h,o(c,:));
    end
end
end

[Austin Hernandez]

thank you, I will do that

[Mrutyunjaya Hiremath]

@ Austin,

Thank you

And, Initialize the values with One NOT Zero ...

c = 1;
m = 1;
u = 1;