How can I write the following matrix?

 if true
A = [x(1)^2 x(1)*y(1) y(1)^2 x(1) 1;
     x(2)^2 x(2)*y(2) y(2)^2 x(2) 1;
     x(3)^2 x(3)*y(3) y(3)^2 x(3) 1;
     x(4)^2 x(4)*y(4) y(4)^2 x(4) 1;
     x(5)^2 x(5)*y(5) y(5)^2 x(5) 1;
     x(6)^2 x(6)*y(6) y(6)^2 x(6) 1;
     x(7)^2 x(7)*y(7) y(7)^2 x(7) 1;
     x(8)^2 x(8)*y(8) y(8)^2 x(8) 1;
     x(9)^2 x(9)*y(9) y(9)^2 x(9) 1;
     x(10)^2 x(10)*y(10) y(10)^2 x(10) 1 ]  
end

The integers 1-10 are meant to be subscripts. I've tried using the syms and repmat functions but have not gotten anywhere further.

[Muhammad Talha]

Try to make this matrix using loop.

Answer 1

[Marta Salas]

x = sym('x', [10 1]);
y = sym('y', [10 1]);
 if true
A = [x(1)^2 x(1)*y(1) y(1)^2 x(1) 1;
     x(2)^2 x(2)*y(2) y(2)^2 x(2) 1;
     x(3)^2 x(3)*y(3) y(3)^2 x(3) 1;
     x(4)^2 x(4)*y(4) y(4)^2 x(4) 1;
     x(5)^2 x(5)*y(5) y(5)^2 x(5) 1;
     x(6)^2 x(6)*y(6) y(6)^2 x(6) 1;
     x(7)^2 x(7)*y(7) y(7)^2 x(7) 1;
     x(8)^2 x(8)*y(8) y(8)^2 x(8) 1;
     x(9)^2 x(9)*y(9) y(9)^2 x(9) 1;
     x(10)^2 x(10)*y(10) y(10)^2 x(10) 1 ]  
end

[Michelle Ashwini]

Right, this works! This is basically the code that I'm working on. Will it be possible to write matrix A in a single line of code maybe?

if true
 %%In this part, we estimate the orbit of the asteroid from the data in 
%  d.x and d.y
x = d.x;
y = d.y;
% The orbit of an asteroid is given by a conic
% (*)     y = c(1)*x.^2 + c(2)*x.*y+c(3)*y.^2+c(4)*x+c(5)
% Find the matrix A and the vector b.
A = sym( x^2 x*y y^2 x 1 )                 % FIX THIS!
b = sym('y', [10,1])                       % FIX THIS!
% Find the size of the matrix A
size(A)= 10 5
end

Inputing the one that you gave on a new script works great but adding it into this file is bringing up errors. Unexpected MATLAB expression .

[Marta Salas]

Do you have any special interest on working on symbolic? I mean, from your code i deduce you have numeric values for x and y, do you want to use them?

[Michelle Ashwini]

No, I don't actually. While reading up, symbolic seemed like the better choice. There are no numerical values for x and y. Its basically a Ac=b matrix where c = [c1 c2 c3 c4 c5], having to solving for c in terms of x and y.

[Marta Salas]

ok. What about this? :

if true
 %%In this part, we estimate the orbit of the asteroid from the data in 
%  d.x and d.y
x = d.x;
y = d.y;
% The orbit of an asteroid is given by a conic
% (*)     y = c(1)*x.^2 + c(2)*x.*y+c(3)*y.^2+c(4)*x+c(5)
% Find the matrix A and the vector b.
x = sym('x', [10 1]);
y = sym('y', [10 1]);
A =[x.^2 x.*y y.^2 x 1]                 % FIX THIS!
b = sym('y', [10,1])                       % FIX THIS!
% Find the size of the matrix A
[r,c]=size(A)
end

[Michelle Ashwini]

I understand what you've written. I created a new script with the code you showed and it gave me the following errors.

Just out of curiosity, is there a way of using repmat here instead? I managed to get it to work with numbers but not with the respective variables.

[Marta Salas]

A =[x.^2 x.*y y.^2 x ones(10,1)]                 % FIX THIS!

sorry about that.

repmat is used to replicate the same array several times. In your case it's not the same array, it's a different value of the array.

[Michelle Ashwini]

This is great! Just tried it out and it ran perfectly! Right! Different value of array. That genuinely makes more sense.

Thank u for your time and effort! Appreciate it!

[Marta Salas]

you're welcome :)

[Michelle Ashwini]

Hi, I tried this again on another computer and got the following error Undefined function 'sym' for input arguments of type 'char'. Is there suppose to be any additional materials installed in it in order for the sym function to work? When i type help syms its says sum not found. How do i go about this?

[Marta Salas]

Type "ver" on the command line. MATLAB lists all the installed toolboxes. Look for Symbolic Math Toolbox. If you don't have the toolbox, you can not use the symbolic functions.

[Michelle Ashwini]

Right. It does not have the symbolic math toolbox installed. Is there another way to to the same thing?

Answer 2

[Azzi Abdelmalek]

 out=[x.^2  x.*y  y.^2.*x  ones(10,1)]

% x and y are column vextors