2 Questions abour geqr2.h

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2 Questions abour geqr2.h

Postby marcoi » Thu Nov 16, 2017 1:50 pm

Hi,
I have 2 questions about geqr2.h:

1) a general question:
for example: https://github.com/langou/latl/blob/mas ... eqr2.h#L69
A[i] is the value of the array corrisponding to the shortest dimension of the matrix A. So, if for example, the shortest dimension of A is the rows number, A[i], as far as I understood, is the value in the i-th row.
I read here: https://github.com/langou/latl/blob/mas ... latl.h#L25 that matrices are implemented as pointers to column-major contiguous arrays. But to which colum of the matrix this i-th row of A[i] (in case m=min(n.m)) belongs to?

I do not understand how the columns (arrays) of a matrix are identified.

For example: in https://github.com/langou/latl/blob/mas ... emv.h#L123
for(j=0;j<n;j++) {
temp=alpha*x[jx];
for(i=0;i<m;i++) {
y[i]+=temp*A[i];
}
}
temp * A[i] is added to the i-th element of the array y . And for all n columns (arrays) of the matrix A[i]
But how to identify a specific element A[j][i] of matrix A?

2) Could you please explain me why (the logic behind it) here: https://github.com/langou/latl/blob/mas ... eqr2.h#L68
every single value of the matrix B, which is equal the matrix A (https://github.com/langou/latl/blob/mas ... eqr2.h#L65), is added first to the column length of the matrix and then added to the iteration counter i https://github.com/langou/latl/blob/mas ... eqr2.h#L74 ?

Looking forward to your kind explanation.
Kind Regards.
Marco
marcoi
 
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