A loop within a loop (for or if)

2 次查看（过去 30 天）
Tim Tolman
Tim Tolman 2016-11-8
编辑： Guillaume 2016-11-8
Hi
I want to create a 3x3 matrix.I have a question regarding changing a value in an equation when i=the lenght of the column, which is 3.
The code so far:
Cm = [Cm1 Cm2 Cm3];
P = 3000
for i=1:3
D2(i) = -(D1(i)+0.5); %mm
Cg(i) = (D1(i)*D2(i))/(D1(i)+D2(i));
a1(i) = 0.721*(P*Cg(i)*Cm(1)).^(1/3); %mm
a2(i) = 0.721*(P*Cg(i)*Cm(2)).^(1/3); %mm
a3(i) = 0.721*(P*Cg(i)*Cm(3)).^(1/3); %mm
end
It works, if i manually change Cm. By doing it like this i can get a 3x3 matrix from:
a = [a1(:) a2(:) a3(:)]
But I want the Cm to change automatically. What to do? :S
Regards Tim
  1 个评论
KSSV
KSSV 2016-11-8
Undefined function or variable 'D1'.
Error in first (line 4) D2(i) = -(D1(i)+0.5); %mm

请先登录，再进行评论。

请先登录，再回答此问题。

回答（2 个）

Ganesh Hegade
Ganesh Hegade 2016-11-8
编辑：Ganesh Hegade 2016-11-8
Hi,
I didn't get exactly what you are trying to do. Hope this works.
Cm = [Cm1 Cm2 Cm3];
P = 3000
for i=1:3 % Better to use length(Cm)
D2(i) = -(D1(i)+0.5); %mm
Cg(i) = (D1(i)*D2(i))/(D1(i)+D2(i));
a1(i) = 0.721*(P*Cg(i)*Cm(i)).^(1/3); %mm
a2(i) = 0.721*(P*Cg(i)*Cm(i)).^(1/3); %mm
a3(i) = 0.721*(P*Cg(i)*Cm(i)).^(1/3); %mm
end
a = [a1', a2', a3' ];
  1 个评论
Guillaume
Guillaume 2016-11-8
编辑：Guillaume 2016-11-8
%Better to use length(Cm)
Actually, better to use numel(Cm). length is dangerous if the input is not a vector.
But of course, even better is not to use a loop...

请先登录，再进行评论。

Guillaume
Guillaume 2016-11-8
I don't particularly understand your question. All I know is you don't need a loop to generate your final a.
I assume your D1 that is not shown is a 1x3 row vector. Then,
D2 = -(D1 + 0.5); %note that numbering variables is never a good idea
Cg = D1 .* D2 ./ (D1 + D2);
%if using R2016b:
a = 0.721 * (P * Cg.' * Cm) .^ (1/3);
%if using an earlier version:
a = 0.721 * (P * bsxfun(@times, Cg.', Cm)) .^ (1/3);
Note that if D1 is a 3x1 column vector, then you don't need to transpose Cg in the a calculation.
If you want to calculate a for different Cm vectors, again you don't need a loop. Simply concatenate all these Cm vectors in the third dimension and the above will still work.

类别

在 Help Center 和 File Exchange 中查找有关 Loops and Conditional Statements 的更多信息

标签

产品

Community Treasure Hunt

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

Start Hunting!

Translated by