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Bug 1560 - Bug in diagonal product for 1x1 matrices
Summary: Bug in diagonal product for 1x1 matrices
Alias: None
Product: Eigen
Classification: Unclassified
Component: Core - matrix products (show other bugs)
Version: 3.4 (development)
Hardware: All All
: Normal Wrong Result
Assignee: Nobody
: 1561 (view as bug list)
Depends on:
Reported: 2018-06-25 08:29 UTC by Gael Guennebaud
Modified: 2019-12-04 17:43 UTC (History)
3 users (show)


Description Gael Guennebaud 2018-06-25 08:29:22 UTC
Reported by Steve Wolter:

When taking the diagonal of a 1x1 matrix and multiplying it with a vector / row vector with an uneven number of cols / rows (e.g. 1x3 or 1x6 with floats), the last chunk's values are incorrect. I've got a minimal example that demonstrates the error with gcc Debian 6.3.0-18+deb9u1 (and older gcc's as well), and Eigen 3.3.4 & 3.3.1 & 3.3.2, but not with Eigen 3.2.9:

#include <iostream>
#include <Eigen/Core>

int main() {
    Eigen::Matrix<float, 1, 1> a;
    Eigen::Matrix<float, 1, Eigen::Dynamic> b(1, 3); 
    std::cerr << a * b << std::endl;              // Correct result: 2 2 2
    std::cerr << a.asDiagonal() * b << std::endl;  // Incorrect result: 2 2 ~0

I couldn't reproduce the error with any size of a except 1x1.
Comment 2 Gael Guennebaud 2018-06-26 06:25:29 UTC
*** Bug 1561 has been marked as a duplicate of this bug. ***
Comment 3 Nobody 2019-12-04 17:43:47 UTC
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