MATLAB: How to store the results from a for loop into a matrix

for loopMATLABmatrix

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?

Best Answer

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.
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