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Bug 834 - (v^T*m)^T != m^T*v
Summary: (v^T*m)^T != m^T*v
Status: RESOLVED DUPLICATE of bug 505
Alias: None
Product: Eigen
Classification: Unclassified
Component: Core - matrix products (show other bugs)
Version: 3.2
Hardware: x86 - 64-bit Linux
: Normal Wrong Result
Assignee: Nobody
URL:
Whiteboard:
Keywords:
Depends on:
Blocks:
 
Reported: 2014-06-26 16:16 UTC by Martin Rueckl
Modified: 2019-12-04 13:27 UTC (History)
2 users (show)


Attachments
test code reproducing the bug (1.33 KB, text/x-c++src)
2014-06-26 16:16 UTC, Martin Rueckl 		no flags Details
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Description Martin Rueckl 2014-06-26 16:16:41 UTC 
Created attachment 471 [details]
test code reproducing the bug

Running the attached code leads to following output, which is wrong (if i'm not completely mistaken)

vector v:2x1:
1
1
matrix m:2x1:
2
2
Using ^T as "transposed"
out1 = (v^T*m)^T : shape: 1x1
out2 = m^T*v     : shape: 1x1
out1(0,0) = 0                       << should also be 4?!?!
out2(0,0) = 4 
out1 == out2: true                  << NO!
Comment 1 Christoph Hertzberg 2014-06-26 16:23:24 UTC 
(v.transpose()*m) is evaluated into a temporary, which gets out of scope when the surrounding ().transpose() is later accessed.

Avoid using auto with Eigen-expressions!

*** This bug has been marked as a duplicate of bug 505 ***
Comment 2 Nobody 2019-12-04 13:27:55 UTC 
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