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

John Stahura

John Stahura (view profile)

님이 질문을 제출함. 20 Sep 2019

님이 편집함. 20 Sep 2019
thoughtGarden

thoughtGarden (view profile)

님이 답변을 채택함.
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?

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R2016a

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thoughtGarden

thoughtGarden (view profile)

님의 답변 20 Sep 2019
thoughtGarden

thoughtGarden (view profile)

님이 편집함. 20 Sep 2019
채택된 답변

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.

댓글 수: 1

20 Sep 2019
Preallocation is preferred over appending datas.

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님의 답변 20 Sep 2019

님이 편집함. 20 Sep 2019

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

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