operations on two different matrices

2021 9 14
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更新时间：2021 9 16
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I need to replace the first row from a matrix A(m.m) by first row from another matrix B(n.n) with different size?

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Walter Roberson
Walter Roberson 2021-9-16

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D0 j=1,8
A(1, j)=D(2,j+1)
end do
Acol = size(A,2);
A(1,:) = D(2,2:Acol+1);
vec = DD1(1,:);
A1(idx,:) = repmat(vec,numel(idx),1);
Acol = size(A,2);
vec = DD1(1,1:Acol);
A1(idx,:) = repmat(vec, numel(idx), 1);

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the cyclist
the cyclist 2021-9-14
编辑：the cyclist 2021-9-15
Ran in:

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Ran in:
Suppose ...
m = 3;
n = 4;
A = magic(m)
A = 3×3
8 1 6 3 5 7 4 9 2
B = magic(n)
B = 4×4
16 2 3 13 5 11 10 8 9 7 6 12 4 14 15 1
The first row of A is a 1x3 row vector, and the first row of B is a 1x4 row vector. What do you want the output to be? Also, what if m had been greater than n?

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Mohamed Hajjaj
Mohamed Hajjaj 2021-9-15
well, I want to replace the the first row of A by the elements 2 3 13 from the first row of B.
In another case, if A: n x n and B: m x m and n +2 = m want to replace A(1, :) by B(1: 2 to n-1).
the cyclist
the cyclist 2021-9-15
Sorry, I still don't understand. Let's take a few specific cases. (The vectors represent the first row.) What should the output be in these cases?
Case 1
A = [8 1 6];
B = [16 2 3 13];
newA = [2 3 13]; % This is what you just said, so confident here.
Is the general rule that you take from the right-hand end?
Case 2
A = [16 2 3 13];
B = [8 1 6];
newA = ?; % What should it be?
Case 3
A = [30 39 48 1 10 19 28];
B = [8 1 6];
newA = ?; % What should it be?
Case 4
A = [8 1 6];
B = [30 39 48 1 10 19 28];
newA = ?; % What should it be?
I'm just trying to understand the general rule, and make sure it covers all possible cases.
Mohamed Hajjaj
Mohamed Hajjaj 2021-9-15
First of all, I would like to thank you for your interesting; the next case may be represent my problem:
If we have A(8,8) and D(10,10) and we can write the following Do-Loop in Fortran:
D0 j=1,8
A(1, j)=D(2,j+1)
end do
is there a simple method to transform into Matlab?
Mohamed Hajjaj
Mohamed Hajjaj 2021-9-15
Soryy, I have tried for the case of A1 and DD1 are of equal size but it did not work; I think may be becaue of A1 is complex while DD1 is real?:
vec = DD1(1,:);
A1(idx,:) = repmat(vec,numel(idx),1);
the cyclist
the cyclist 2021-9-15
Sorry, but your last two comments are just confusing to me.
You did not respond to my questions. What are the results for Case 1, Case 2, etc?
I don't know Fortran anymore, so cannot interpret that.
Why are you suddenly introducing new variables (D, DD1, idx)? Your original question seemed very simple, about filling in the first row of a matrix A, from the first row of a matrix B. It seems to be getting more and more complicated with every comment.
Mohamed Hajjaj
Mohamed Hajjaj 2021-9-16
The first case is the nearest one to my problem.The symbols D, DD1, ...are matrices, but I'm sorry about any confusion. Would you please help me for the first case?

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