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Bug 1265 - HouseholderQR description and example do not match.
Summary: HouseholderQR description and example do not match.
Status: RESOLVED FIXED
Alias: None
Product: Eigen
Classification: Unclassified
Component: Documentation (show other bugs)
Version: 3.3 (current stable)
Hardware: All All
: Normal Documentation
Assignee: Nobody
URL:
Whiteboard:
Keywords:
Depends on:
Blocks:
 
Reported: 2016-07-28 16:32 UTC by EMM
Modified: 2016-08-22 21:27 UTC (History)
5 users (show)



Attachments

Description EMM 2016-07-28 16:32:36 UTC
HouseholderQR states that .solve() for a matrix b in solving Ax=b is not yet implemented, specifically:
"Note
    The case where b is a matrix is not yet implemented. Also, this code is space inefficient.
"

But, the example provided to solve mx=y uses all 3x3, returning the text:

"Here is the matrix m:
  0.68  0.597  -0.33
-0.211  0.823  0.536
 0.566 -0.605 -0.444
Here is the matrix y:
  0.108   -0.27   0.832
-0.0452  0.0268   0.271
  0.258   0.904   0.435
Here is a solution x to the equation mx=y:
 0.609   2.68   1.67
-0.231  -1.57 0.0713
  0.51   3.51   1.05
"

So, I conclude that either:

1) The documentation is lagging the code, and the Note should be removed or corrected to describe the actual limitations on RHS when solve'ing.

2) The example was re-used (from some other .solve() usage) to show the interface, but should be modified to show a vector y.

3) I just didn't understand correctly...in which case I apologize.

I followed the link to "development branch documentation", which shows 3.2.93, and that was the same as the 3.2.9, with the inconsistency described above.

Thank you for the generally excellent documentation!
Comment 1 Christoph Hertzberg 2016-07-28 16:49:33 UTC
You can generally be certain the code snippet is working and the given output is the actual output of the operation (we compile the snippets and run them when generating the documentation).
Therefore:
> 1) The documentation is lagging the code, and the Note should be removed or
> corrected to describe the actual limitations on RHS when solve'ing.

I'm not sure however, what is (or was) meant by "space inefficient" here.
Quite likely this is obsolete as well (at least for the 3.3 branch).

Also, this seems to be outdated for some other decompositions, too.
Comment 2 Gael Guennebaud 2016-08-22 21:27:54 UTC
Those notes are obsolete:

default: https://bitbucket.org/eigen/eigen/commits/5a47e5a5b02e/
3.2:     https://bitbucket.org/eigen/eigen/commits/a8ba94a7aa3c/

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