Adding Matrices to make Bigger Matrix

25 次查看（过去 30 天）
Chris Dan
Chris Dan 2019-11-6
评论： Walter Roberson 2019-11-7
Hello
I have a problem related to FEM. I want to add two stiffness matrices. Such as
A = [ 1 -1;
-1 1];
and
B = [ 2 -2;
-2 2];
The result which I should get is
C = [1 -1 0;
-1 3 -2;
0 -2 2];
C is a 3x3 matrix and A is a 2x2 matrix, B is also a 2x2 matrix
Does anybody know how to do it in a loop and how to expand it to more matrices, such as if I have 3 or 4 matrices instead of 2 and I want to add them this way.

请先登录，再回答此问题。

采纳的回答

the cyclist
the cyclist 2019-11-6
编辑：the cyclist 2019-11-6
Here is a straightforward way to do it with a for loop:
A{1} = [ 1 -1;
-1 1];
A{2} = [ 2 -2;
-2 2];
A{3} = [ 3 -3;
-3 3];
numberMatrices = size(A,2);
output = zeros(numberMatrices+1);
for na = 1:numberMatrices
output(na:na+1,na:na+1) = output(na:na+1,na:na+1) + A{na};
end
It relies on having stored your input arrays sensibly in a cell array, rather than as variables named A,B,C,..., Z.
  4 个评论
显示 2更早的评论
the cyclist
the cyclist 2019-11-7
Yes, what Stephen wrote. Although you can still make my solution work, if you do
B = [ 1 -1;
-1 1];
C = [ 2 -2;
-2 2];
D = [ 3 -3;
-3 3];
A = {B,C,D};
before using my algorithm.
Walter Roberson
Walter Roberson 2019-11-7
For larger matrices you need to define whether the offset to add them at is down by 1 diagonally each time, or the the rule is to overlap just the last entry.

请先登录，再进行评论。

更多回答（1 个）

Walter Roberson
Walter Roberson 2019-11-7
It is probably easiest to intialize C to zeros() and then loop over a cell array {A, B, third, fourth} adding them into the appropriate section of C cumulatively.
There are other options, but they are not nearly as clear.

类别

在 Help Center 和 File Exchange 中查找有关 Operating on Diagonal Matrices 的更多信息

标签

Community Treasure Hunt

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

Start Hunting!

Translated by