How to grow a vector in a loop?

6 visualizaciones (últimos 30 días)
Saurabh Tyagi
Saurabh Tyagi el 15 de Oct. de 2021
Comentada: Saurabh Tyagi el 15 de Oct. de 2021
So I have two nested loops
for ii = 1:ldiv+1
for jj = 1:sdiv+1
x_m = sb_panel(ii,jj).xm;
y_m = sb_panel(ii,jj).ym;
z_m = sb_panel(ii,jj).zm;
for kk = 1:ldiv+1
for ll = 1:sdiv+1
x_a = sb_panel(kk,ll).xa;
y_a = sb_panel(kk,ll).ya;
z_a = sb_panel(kk,ll).za;
x_b = sb_panel(kk,ll).xb;
y_b = sb_panel(kk,ll).yb;
z_b = sb_panel(kk,ll).zb;
aa = 1/(((x_m-x_a)*(y_m-y_b)-(x_m-x_b)*(y_m-y_a)));
bb = ((x_b-x_a)*(x_m-x_a)+(y_b-y_a)*(y_m-y_a))/sqrt((x_m-x_a)^2+(y_m-y_a)^2);
cc = ((x_b-x_a)*(x_m-x_b)+(y_b-y_a)*(y_m-y_b))/sqrt((x_m-x_b)^2+(y_m-y_b)^2);
dd = (1/(y_a-y_m))*(1+(x_m-x_a)/sqrt((x_m-x_a)^2+(y_m-y_a)^2));
ee = (1/(y_b-y_m))*(1+(x_m-x_b)/sqrt((x_m-x_b)^2+(y_m-y_b)^2));
coeff = [(aa*(bb-cc)+dd-ee)];
end
end
end
end
The problem is the innermost loop runs as many times as it's supposed to and assigns the last value to 'coeff' but what I want is that each time it runs, it assigns a value to coeff, and then assign the value in next cell when it runs again.

Respuesta aceptada

Matt J
Matt J el 15 de Oct. de 2021
Editada: Matt J el 15 de Oct. de 2021
You could just vectorize everything.
x_m = [sb_panel.xm];
y_m = [sb_panel.ym];
z_m = [sb_panel.zm];
x_a = [sb_panel.xa].';
y_a = [sb_panel.ya].';
z_a = [sb_panel.za].';
x_b = [sb_panel.xb].';
y_b = [sb_panel.yb].';
z_b = [sb_panel.zb].';
aa = 1./(((x_m-x_a).*(y_m-y_b)-(x_m-x_b).*(y_m-y_a)));
bb = ((x_b-x_a).*(x_m-x_a)+(y_b-y_a).*(y_m-y_a))./sqrt((x_m-x_a).^2+(y_m-y_a).^2);
cc = ((x_b-x_a).*(x_m-x_b)+(y_b-y_a).*(y_m-y_b))./sqrt((x_m-x_b).^2+(y_m-y_b).^2);
dd = (1./(y_a-y_m)).*(1+(x_m-x_a)./sqrt((x_m-x_a).^2+(y_m-y_a).^2));
ee = (1./(y_b-y_m)).*(1+(x_m-x_b)./sqrt((x_m-x_b).^2+(y_m-y_b).^2));
coeff = reshape( aa.*(bb-cc)+dd-ee , [],1);
  2 comentarios
Saurabh Tyagi
Saurabh Tyagi el 15 de Oct. de 2021
Yikes, this worked PERFECTLY. Thank you so much for you time. Can you point out my mistakes and more insight into what you did?
Matt J
Matt J el 15 de Oct. de 2021
Can you point out my mistakes
In your original approach? My other answer describes how to get that to work.
and more insight into what you did?
we first collected the fields of your stucture into vectors
s(1).a=10; s(2).a=20; s(3).a=30;
v=[s.a]
v = 1×3
10 20 30
Then, you just use implicit expansion for all the arithmetic operations, e.g.,
v+(1:4).'
ans = 4×3
11 21 31 12 22 32 13 23 33 14 24 34

Iniciar sesión para comentar.

Más respuestas (2)

Scott MacKenzie
Scott MacKenzie el 15 de Oct. de 2021
One approach is to declare coeff as an empty array before the first for-statement:
coeff = [];
then add new values to the end of the coeff array as follows:
coeff = [coeff, (aa*(bb-cc)+dd-ee)];
  2 comentarios
Saurabh Tyagi
Saurabh Tyagi el 15 de Oct. de 2021
I tried doing that, didn't work. I do get correct answers, but in reverse order. Like if it should be [A B C D], I get [D C B A]
Scott MacKenzie
Scott MacKenzie el 15 de Oct. de 2021
In that case, just reverse the order in the assignment:
coeff = [(aa*(bb-cc)+dd-ee), coeff];

Iniciar sesión para comentar.


Matt J
Matt J el 15 de Oct. de 2021
Editada: Matt J el 15 de Oct. de 2021
coef=nan((ldiv+1)^2*(sdiv+1)^2,1); %PRE-ALLOCATE
mm=0;
for ii = 1:ldiv+1
for jj = 1:sdiv+1
...
for kk = 1:ldiv+1
for ll = 1:sdiv+1
....
mm=mm+1;
coeff(mm) = [(aa*(bb-cc)+dd-ee)];
end
end
end
end
  1 comentario
Saurabh Tyagi
Saurabh Tyagi el 15 de Oct. de 2021
Oh that "mm" thing was such an elegant fix to this problem. I have been breaking my head over it for more than a day.

Iniciar sesión para comentar.

Categorías

Más información sobre Programming en Help Center y File Exchange.

Productos


Versión

R2021b

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by