How to store the results from a for loop into a matrix?

clear all
clc
F = 2; 
x = [.1:.05:1.9];
for i = x;
    theta1 = atan((2-i)/1);
    theta2 = atan(1/(2-i));
    theta3 = atan(1/i);
    A = [-1 -cos(theta2) 0 0 0 0 0 0 0 0; %Fab
        0 sin(theta2) 0 0 0 0 0 0 0 0; %Fac
        1 0 -1 0 0 0 0 0 0 0; %Fbd
        0 0 0 1 0 0 0 0 0 0; %Fbc
        0 sin(theta1) 0 0 -1 -cos(theta3) 0 0 0 0; %Fce
        0 -cos(theta1) 0 -1 0 -sin(theta3) 0 0 0 0; %Fcd
        0 0 1 0 0 cos(theta3) -1 0 0 0; %Dx
        0 0 0 0 0 sin(theta3) 0 1 0 0; %Fde
        0 0 0 0 1 0 0 0 -1 0; %Ex
        0 0 0 0 0 0 0 -1 0 1]; %Ey
        
    b = [0 F 0 F/2 0 0 0 0 0 0]';
    Reactions = A\b
end

How do i store the "Reactions" results from each iteration of the loop into one matrix?

Answer 1

[thoughtGarden]

Note that there area some poor practices in place here, but with the most minimal change to what you already have is to create a blank matrix Reactions and then add each column to that matrix as they are developed.

clear all
clc
F = 2; 
x = [.1:.05:1.9];

Reactions = [];

for i = x;
    theta1 = atan((2-i)/1);
    theta2 = atan(1/(2-i));
    theta3 = atan(1/i);
    A = [-1 -cos(theta2) 0 0 0 0 0 0 0 0; %Fab
        0 sin(theta2) 0 0 0 0 0 0 0 0; %Fac
        1 0 -1 0 0 0 0 0 0 0; %Fbd
        0 0 0 1 0 0 0 0 0 0; %Fbc
        0 sin(theta1) 0 0 -1 -cos(theta3) 0 0 0 0; %Fce
        0 -cos(theta1) 0 -1 0 -sin(theta3) 0 0 0 0; %Fcd
        0 0 1 0 0 cos(theta3) -1 0 0 0; %Dx
        0 0 0 0 0 sin(theta3) 0 1 0 0; %Fde
        0 0 0 0 1 0 0 0 -1 0; %Ex
        0 0 0 0 0 0 0 -1 0 1]; %Ey
        
    b = [0 F 0 F/2 0 0 0 0 0 0]';
    Reactions = [Reactions, A\b];
end

a better solution would be to loop over index value (instead of the values of x) and preallocate the matrix.

clear all
clc
F = 2; 
x = [.1:.05:1.9];

Reactions = zeros(10,size(x,1));

for ii = 1:length(x)
    theta1 = atan((2-x(ii))/1);
    theta2 = atan(1/(2-x(ii)));
    theta3 = atan(1/x(ii));
    A = [-1 -cos(theta2) 0 0 0 0 0 0 0 0; %Fab
        0 sin(theta2) 0 0 0 0 0 0 0 0; %Fac
        1 0 -1 0 0 0 0 0 0 0; %Fbd
        0 0 0 1 0 0 0 0 0 0; %Fbc
        0 sin(theta1) 0 0 -1 -cos(theta3) 0 0 0 0; %Fce
        0 -cos(theta1) 0 -1 0 -sin(theta3) 0 0 0 0; %Fcd
        0 0 1 0 0 cos(theta3) -1 0 0 0; %Dx
        0 0 0 0 0 sin(theta3) 0 1 0 0; %Fde
        0 0 0 0 1 0 0 0 -1 0; %Ex
        0 0 0 0 0 0 0 -1 0 1]; %Ey
        
    b = [0 F 0 F/2 0 0 0 0 0 0]';
    Reactions(:,ii) = A\b;
end

disp(Reactions)

Both are valid, but the later is more efficient and clear to future readers.

[madhan ravi]

Preallocation is preferred over appending datas.

https://in.mathworks.com/help/matlab/matlab_prog/preallocating-arrays.html - for the importance of preallocation

Answer 2

[madhan ravi]

F = 2; 
x = .1:.05:1.9;
Reactions = cell(numel(x),1);
b = [0 F 0 F/2 0 0 0 0 0 0]'; % there's no point in defining it over and over again inside the loop.
for ii = 1:numel(x);
    theta1 = atan((2-x(ii))/1);
    theta2 = atan(1/(2-x(ii)));
    theta3 = atan(1/x(ii));
    A = [-1 -cos(theta2) 0 0 0 0 0 0 0 0; %Fab
        0 sin(theta2) 0 0 0 0 0 0 0 0; %Fac
        1 0 -1 0 0 0 0 0 0 0; %Fbd
        0 0 0 1 0 0 0 0 0 0; %Fbc
        0 sin(theta1) 0 0 -1 -cos(theta3) 0 0 0 0; %Fce
        0 -cos(theta1) 0 -1 0 -sin(theta3) 0 0 0 0; %Fcd
        0 0 1 0 0 cos(theta3) -1 0 0 0; %Dx
        0 0 0 0 0 sin(theta3) 0 1 0 0; %Fde
        0 0 0 0 1 0 0 0 -1 0; %Ex
        0 0 0 0 0 0 0 -1 0 1]; %Ey
    Reactions{ii} = A\b;
end
celldisp(Reactions)
cat(2,Reactions{:}) % if you want a matrix