matlab efficient copying of matrix
Domanda
I have matrix (a) with (1:10),<10 x 1> double. I would like to copy the values and rearrange them column wise into another matrix var. (b). See example below. Also, what method would be most efficient at this task?
matrix a matrix b
1 1
2 2 2
3 3 3 3
4 4 4 4 4
5 5 5 5 5 5
6 6 6 6 6 6 6
7 7 7 7 7 7 7 7
8 8 8 8 8 8 8 8 8
9 9 9 9 9 9 9 9 9 9
10 10 10 10 10 10 10 10 10 10 10
update: Hi once again Amro. How about if I wanted to define which values to copy. See below example:
matrix a matrix b
column: 1 2 3 4 5 6 7
1 1
2 2 2
3 3 3
4 4
5 5
6 6
7 7
8 8
9 9
10 10 10
Soluzione
Try:
>> a = (1:10)'
a =
1
2
3
4
5
6
7
8
9
10
>> b = tril(repmat(a,1,10))
b =
1 0 0 0 0 0 0 0 0 0
2 2 0 0 0 0 0 0 0 0
3 3 3 0 0 0 0 0 0 0
4 4 4 4 0 0 0 0 0 0
5 5 5 5 5 0 0 0 0 0
6 6 6 6 6 6 0 0 0 0
7 7 7 7 7 7 7 0 0 0
8 8 8 8 8 8 8 8 0 0
9 9 9 9 9 9 9 9 9 0
10 10 10 10 10 10 10 10 10 10
Altri suggerimenti
I think in the second matrix you specified you made an error. I'm assuming you wanted to do something like this:
b =
1 0 0 0 0 0
2 2 0 0 0 0
0 3 3 0 0 0
0 0 4 4 0 0
0 0 0 5 5 0
0 0 0 0 6 6
this is simple to do:
%define vector of arbitrary length
a=1:6;
%generate b with shifted diagonal matrices
b=diag(a)+diag(a(2:end),-1);
the second argument of diag just shifts the resulting diagonal.
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