How do I store the changing values of a variable (generated in a for loop) into a single file without overwriting the previous one?

For example:

n = 100;
for ii = 1 : n
areatriangle = .5*((ii/2)*ii);
end

In the case above, I want to store all the outcomes/iterations of areatriangle, not just the last one. How do I do this?

Thanks in advance for your help!

Answer 1

[Alex Mcaulley]

n = 100;
areatriangle = zeros(1,n)
for ii = 1 : n
    areatriangle(ii) = .5*((ii/2)*ii);
end

or:

areatriangle = .5/2*(1:n).^2;

[Steve]

Thanks Alex. In my actual code (see below), I can't seem to get this to work for the output variables (i.e., ThetaInDegrees_a, ThetaInDegrees_b, ThetaInDegrees_c), where I need 10 angles for each pt (10 x 953). Can you help with me this? Thanks in advance for any help you could offfer.

close all;
clearvars;
load('F_points.mat');
load('fpep.mat');
xy = F_points';
n = 10; % Find the n closest values (excluding the point selected)
for pt = 1 : 953
dist = sqrt((xy(:,1)-xy(pt,1)).^2 + (xy(:,2)-xy(pt,2)).^2);
[~, ascendIdx] = sort(dist); 
ascendIdx(ascendIdx==pt) = [];  %remove the pt point
xyNearest = xy(ascendIdx(1:n),:);
adirector_x = ([fpep(pt,1) - fpep(pt,7)]);
adirector_y = ([fpep(pt,2) - fpep(pt,8)]);
bdirector_x = ([fpep(pt,3) - fpep(pt,7)]);
bdirector_y = ([fpep(pt,4) - fpep(pt,8)]);
cdirector_x = ([fpep(pt,5) - fpep(pt,7)]);
cdirector_y = ([fpep(pt,6) - fpep(pt,8)]);
vector_a = [adirector_x adirector_y];
vector_b = [bdirector_x bdirector_y];
vector_c = [cdirector_x cdirector_y];
chordx = ([xyNearest(:,1) - xy(pt,1)]);
chordy = ([xyNearest(:,2) - xy(pt,2)]);
chordxy = [chordx chordy];
    for j = 1 : n
        CosTheta_a(j) = dot(vector_a,chordxy(j,:))/(norm(vector_a)*norm(chordxy(j,:)));
        CosTheta_b(j) = dot(vector_b,chordxy(j,:))/(norm(vector_b)*norm(chordxy(j,:)));
        CosTheta_c(j) = dot(vector_c,chordxy(j,:))/(norm(vector_c)*norm(chordxy(j,:)));
        ThetaInDegrees_a(j) = acosd(CosTheta_a(j));
        ThetaInDegrees_b(j) = acosd(CosTheta_b(j));
        ThetaInDegrees_c(j) = acosd(CosTheta_c(j));
    end
end

[Alex Mcaulley]

In this case you need to store the result in a matrix

for j = 1 : n
    CosTheta_a(j,pt) = dot(vector_a,chordxy(j,:))/(norm(vector_a)*norm(chordxy(j,:)));
    CosTheta_b(j,pt) = dot(vector_b,chordxy(j,:))/(norm(vector_b)*norm(chordxy(j,:)));
    CosTheta_c(j,pt) = dot(vector_c,chordxy(j,:))/(norm(vector_c)*norm(chordxy(j,:)));
    ThetaInDegrees_a(j,pt) = acosd(CosTheta_a(j));
    ThetaInDegrees_b(j,pt) = acosd(CosTheta_b(j));
    ThetaInDegrees_c(j,pt) = acosd(CosTheta_c(j));
end

Don't forget to initialize every variable before the loops to increase the speed:

CosTheta_a = zeros(n,953) 
%And so on

[Steve]

Thanks again Alex. I tried running this change and it just gave me the first 10 angles 953 times. Any idea on what's going wrong? Thanks again!

[Alex Mcaulley]

It works for me! Where are you initializing the variables?

close all;
clearvars;
load('F_points.mat');
load('fpep.mat');
xy = F_points';
n = 10; % Find the n closest values (excluding the point selected)

CosTheta_a = zeros(n,953);
CosTheta_b = zeros(n,953); 
CosTheta_c = zeros(n,953); 
ThetaInDegrees_a = zeros(n,953); 
ThetaInDegrees_b = zeros(n,953); 
ThetaInDegrees_c = zeros(n,953);

for pt = 1 : 953
dist = sqrt((xy(:,1)-xy(pt,1)).^2 + (xy(:,2)-xy(pt,2)).^2);
[~, ascendIdx] = sort(dist); 
ascendIdx(ascendIdx==pt) = [];  %remove the pt point
xyNearest = xy(ascendIdx(1:n),:);
adirector_x = ([fpep(pt,1) - fpep(pt,7)]);
adirector_y = ([fpep(pt,2) - fpep(pt,8)]);
bdirector_x = ([fpep(pt,3) - fpep(pt,7)]);
bdirector_y = ([fpep(pt,4) - fpep(pt,8)]);
cdirector_x = ([fpep(pt,5) - fpep(pt,7)]);
cdirector_y = ([fpep(pt,6) - fpep(pt,8)]);
vector_a = [adirector_x adirector_y];
vector_b = [bdirector_x bdirector_y];
vector_c = [cdirector_x cdirector_y];
chordx = ([xyNearest(:,1) - xy(pt,1)]);
chordy = ([xyNearest(:,2) - xy(pt,2)]);
chordxy = [chordx chordy]; 
    for j = 1 : n
        CosTheta_a(j,pt) = dot(vector_a,chordxy(j,:))/(norm(vector_a)*norm(chordxy(j,:)));
        CosTheta_b(j,pt) = dot(vector_b,chordxy(j,:))/(norm(vector_b)*norm(chordxy(j,:)));
        CosTheta_c(j,pt) = dot(vector_c,chordxy(j,:))/(norm(vector_c)*norm(chordxy(j,:)));
        ThetaInDegrees_a(j,pt) = acosd(CosTheta_a(j));
        ThetaInDegrees_b(j,pt) = acosd(CosTheta_b(j));
        ThetaInDegrees_c(j,pt) = acosd(CosTheta_c(j));
    end
end

[Steve]

I just copied your code and ran it; this is what I got for ThetaInDegrees_a (see screenshot):

[Alex Mcaulley]

Ohhh yes, you need to change the following lines in the last loop:

ThetaInDegrees_a(j,pt) = acosd(CosTheta_a(j,pt));
ThetaInDegrees_b(j,pt) = acosd(CosTheta_b(j,pt));
ThetaInDegrees_c(j,pt) = acosd(CosTheta_c(j,pt));

[Steve]

Bingo! You're amazing. Thank you so much!