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From: | anonymous |
Subject: | [Octave-bug-tracker] [bug #55256] Wrong result raise a non-diagonalizable matrix by a fractional exponent |
Date: | Thu, 20 Dec 2018 14:54:03 -0500 (EST) |
User-agent: | Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:64.0) Gecko/20100101 Firefox/64.0 |
URL: <https://savannah.gnu.org/bugs/?55256> Summary: Wrong result raise a non-diagonalizable matrix by a fractional exponent Project: GNU Octave Submitted by: None Submitted on: Thu 20 Dec 2018 07:54:01 PM UTC Category: Octave Function Severity: 3 - Normal Priority: 5 - Normal Item Group: None Status: None Assigned to: None Originator Name: Volker Becker Originator Email: address@hidden Open/Closed: Open Discussion Lock: Any Release: 4.4.1 Operating System: Any _______________________________________________________ Details: If raise a non-diagonalizable matrix to a fractional power, the result is wrong. For example: >> A=[1 1 1; 0 1 1; 0 0 1] A = 1 1 1 0 1 1 0 0 1 >> B = A^0.5 B = 1.00000 0.00000 0.00000 0.00000 1.00000 0.00000 0.00000 0.00000 1.00000 So B*B is obiously not equal to A. probaly the result will be calculated by diagonalistion of the matrix which fails when the matrix is non-diagonalizable. The correct result (due to wolfram aplha) would be C=[1 0.5 0.375; 0 1 0.5; 0 0 1] C = 1.00000 0.50000 0.37500 0.00000 1.00000 0.50000 0.00000 0.00000 1.00000 >> C*C ans = 1 1 1 0 1 1 0 0 1 _______________________________________________________ Reply to this item at: <https://savannah.gnu.org/bugs/?55256> _______________________________________________ Message sent via Savannah https://savannah.gnu.org/
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