All my Values not getting stored. Only my Last Value is getting stored

Hi All,

Below attached is my code. In this code I am trying to produce various iterations of theta however only the last value of theta is getting stored in the loop. How can I fix this? Furthermore I am trying to save it into an excel spreadsheet however as it is only producing the last value, only one value is stored.

Thank You,

[Cameron]

Which variable are you trying to store? theta_average?

[Tishan Anantharajah]

Yes I am trying to store theta_average

Answer 1

[Matt J]

A loop will not accumulate a vector of results unless you tell it where in the vector the result is to be placed, e.g.,

for i=1:5
    
    theta(i)=i^2;
    
end
theta

theta = 1×5

1 4 9 16 25

Compare this to,

for i=1:5
    
    alpha=i^2;
    
end
alpha

alpha = 25

[Tishan Anantharajah]

How would my code be changed accordingly to accumulate this?

[Matt J]

As in my example above. You currently have no indexing on the left hand side of your assignment statements that tell where your data is to be stored.

Answer 2

[Cameron]

You need to save values of theta_average, so you can index it this way. You go through a while loop then save it when you need to by indexing.

k = 0 ;
theta_average = []; %preallocate this variable, then save it at the end
while true
hold on

va = 1;
mu = 0;

a = rand([3,1]);
b = rand([3,1]);
c = rand([3,1]);
d = rand([3,1]);


a_real = (1/sqrt(2*pi)*exp((-a.^2)/2));
b_real = (1/sqrt(2*pi)*exp((-b.^2)/2));
c_real = (1/sqrt(2*pi)*exp((-c.^2)/2));
d_real = (1/sqrt(2*pi)*exp((-d.^2)/2));

v1 = b_real-a_real;
v2 = c_real-a_real;
v3 = c_real-b_real;
v4 = d_real-c_real;
t = linspace(0,1);

v1x = v1(1)*t + a_real(1) ; v1y = v1(2)*t + a_real(2); v1z = v1(3)*t + a_real(3);
v2x = v2(1)*t + b_real(1) ; v2y = v2(2)*t + b_real(2); v2z = v2(3)*t + b_real(3);
v3x = v3(1)*t + c_real(1) ; v3y = v3(2)*t + c_real(2); v3z = v3(3)*t + c_real(3);
v4x = v4(1)*t + d_real(1) ; v4y = v4(2)*t + d_real(2); v4z = v4(3)*t + d_real(3);

grid on; rotate3d on
plot3(a_real(1),a_real(2),a_real(3),'or')
hold on
plot3(b_real(1),b_real(2),b_real(3),'or')

plot3(c_real(1),c_real(2),c_real(3),'or')

plot3(d_real(1),d_real(2),d_real(3),'or')

plot3(v1x,v1y,v1z,'b','linew',2)

plot3(v2x,v2y,v2z,'b','linew',2)

plot3(v3x,v3y,v3z,'b','linew',2)

plot3(v4x,v4y,v4z,'b','linew',2)
% Only 6 variations are possible for 4 points.
n_t = cross(v1,v2); n = n_t/norm(n_t);
% Did not cross v2 and v3 because they produce the same normal.
n2 = cross(v1,v3); n2 = n2/norm(n2);
% Why is n3 so large? How should I pick which normal to use out of a
% combination?
n3 = cross(v1,v4); n3 = n3/norm(n3);
n4 = cross(v2,v4); n4 = n4/norm(n4);
n5 = cross(v3,v4); n5 = n5/norm(n5);
n_average = (n3+n4+n5)./3;

nx = n(1)*t + a_real(1) ; ny = n(2)*t + a_real(2); nz = n(3)*t + a_real(3);
n3x = n3(1)*t + a_real(1) ; n3y = n3(2)*t + a_real(2); n3z = n3(3)*t + a_real(3);
n4x = n4(1)*t + a_real(1) ; n4y = n4(2)*t + a_real(2); n4z = n4(3)*t + a_real(3);
n5x = n5(1)*t + a_real(1) ; n5y = n5(2)*t + a_real(2); n5z = n5(3)*t + a_real(3);
n_averagex = n_average(1)*t + a_real(1) ; n_averagey = n_average(2)*t + a_real(2); n_averagez = n_average(3)*t + a_real(3);

plot3(nx,ny,nz,'r','LineWidth',2) 
plot3(n3x,n3y,n3z,'r','LineWidth',2) 
plot3(n4x,n4y,n4z,'r','LineWidth',2) 
plot3(n5x,n5y,n5z,'r','LineWidth',2) 
plot3(n_averagex,n_averagey,n_averagez,'r','LineWidth',2) 
% Why is this not plotting?

[x,y] = meshgrid(1:100:8000);
% plane = n(1)(x-a(1)) + n(2)(y-a(2)) + n(3)(z-a(3)) = 0

z = ((n(1).*(x-a_real(1))) + (n(2).*(y-a_real(2))) - (n(3)*a_real(3)))./-(n(3));
z3 = ((n3(1).*(x-a_real(1))) + (n3(2).*(y-a_real(2))) - (n3(3)*a_real(3)))./-(n3(3));
z4 = ((n4(1).*(x-a_real(1))) + (n4(2).*(y-a_real(2))) - (n4(3)*a_real(3)))./-(n4(3));
z5 = ((n5(1).*(x-a_real(1))) + (n5(2).*(y-a_real(2))) - (n5(3)*a_real(3)))./-(n5(3));
z_average = ((n_average(1).*(x-a_real(1))) + (n_average(2).*(y-a_real(2))) - (n_average(3)*a_real(3)))./-(n_average(3));
hold on
grid on; rotate3d on
plot3(v3x,v3y,v3z,'b','linew',2)

surf(x,y,z)
surf(x,y,z3)
surf(x,y,z4)
surf(x,y,z5)
surf(x,y,z_average)

nv = n_t.*n_t;
dp = sum(nv);
mag = sqrt(dp);

n3v = n3.*n3;
dp3 = sum(n3v);
mag3 = sqrt(dp3);

n4v = n4.*n4;
dp4 = sum(n4v);
mag4 = sqrt(dp4);

n5v = n5.*n5;
dp5 = sum(n5v);
mag5 = sqrt(dp5);

n_averagev = n_average.*n_average;
dp_average = sum(n_averagev);
mag_average = sqrt(dp_average);

theta2 = acosd((dot(n_t,n3v))/(mag*mag3));
theta3 = acosd((dot(n_t,n4v))/(mag*mag4));
theta4 = acosd((dot(n_t,n5v))/(mag*mag5));
theta_average(end+1,1) = acosd((dot(n_t,n_averagev))/(mag*mag_average));


k = k + 1 ;
    if k > randi(5,1)
        break
    end
    disp(k)
    disp(theta_average)
    writematrix(theta_average,filename,'Sheet',1,'Range','B2:B10')
    
end

[Tishan Anantharajah]

I am very new to Matlab how would i get the values to save