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Bug 839 - Wrong 1x1 triangular matrix-vector product
Summary: Wrong 1x1 triangular matrix-vector product
Status: RESOLVED FIXED
Alias: None
Product: Eigen
Classification: Unclassified
Component: Core - matrix products (show other bugs)
Version: unspecified
Hardware: All All
: Normal Wrong Result
Assignee: Nobody
URL:
Whiteboard:
Keywords:
Depends on:
Blocks: 840
  Show dependency tree / graph
 
Reported: 2014-07-07 14:28 UTC by Chen-Pang He
Modified: 2019-12-04 13:29 UTC (History)
2 users (show)


Attachments
Demo reproducing the bug (955 bytes, text/x-csrc)
2014-07-07 14:28 UTC, Chen-Pang He 		no flags Details
View All Add an attachment (proposed patch, testcase, etc.)

Description Chen-Pang He 2014-07-07 14:28:02 UTC 
Created attachment 473 [details]
Demo reproducing the bug

Our internal::triangular_matrix_vector_product is specialized for triangular matrix-vector product.  When 1x1 times 1xn, it ends prematurely by computing only one entry.

The below is the output from the program compiled with the attachment.

Matrix:
 0.144509
0.0973679
-0.228021
 0.190039
-0.105256
-0.131808
0.0489002
 0.160188

Triangular:
0.144509
       0
       0
       0
       0
       0
       0
       0

?TRMV:
0.144509
       0
       0
       0
       0
       0
       0
       0

?TRMM:
 0.144509
0.0973679
-0.228021
 0.190039
-0.105256
-0.131808
0.0489002
 0.160188
Comment 1 Chen-Pang He 2014-07-08 08:13:34 UTC 
I see where the problem is.

When TriangularProduct invokes internal::trmv_selector, side information is lost.  We assumed that if the non-triangular is column-vector then the triangular is on the left.  However, it is possible that the triangular is row-vector on the right.

I am working on a patch to internal::trmv_selector.
Comment 2 Chen-Pang He 2014-07-08 21:38:55 UTC 
I found that no refactorization is needed.  I have made a pull request.
https://bitbucket.org/eigen/eigen/pull-request/72/fix-bug-839
Comment 4 Nobody 2019-12-04 13:29:57 UTC 
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