Problem 972. Set a diagonal

Created by Nicholas Howe

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Given a matrix M, row vector v of appropriate length, and diagonal index d (where 0 indicates the main diagonal and off-diagonals are identified by positive and negative integers), return a new matrix where the specified diagonal of M is replaced by v. You may assume that v is the correct length for the specified diagonal. If d is not provided, assume it is zero.
For example,
M = magic(5);
setDiagonal(M,1:4,-1)
ans =
  17    24     1     8    15
   1     5     7    14    16
   4     2    13    20    22
  10    12     3    21     3
  11    18    25     4     9

Solve

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Last Solution submitted on Dec 22, 2025

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Nicholas Howe on 9 Oct 2012

Added new test case 9 Oct. 2012

Ned Gulley on 10 Oct 2012

Are you missing some text from your example?

Ned Gulley on 10 Oct 2012

Test suggestion: Stick a zero in one of your v vectors and you'll eliminate some of the shorter answers.

Jean-Marie Sainthillier on 11 Oct 2012

Yes. All solutions with find don't work with 0 in v.

Nicholas Howe on 14 Jan 2013

Thanks for the suggestions -- I updated the text, added a new test case and rescored.

yurenchu on 15 Apr 2017

@Nicholas Howe: The test suggestion meant: stick a 0 in v, and this 0 is meant to replace an entry of M that was unequal to 0. In other words: the new test-case doesn't make a difference (and hence is useless) if M is a null-matrix.

Ahsan Naeem on 10 Jun 2017

The cases with d=0 are working for me but your test cases are giving error..... What's this?

Riccardo Dessì on 25 Jun 2018

please, when you make use of test cases with floating point numbers specify a common precision, otherwise is impossible to pass the suite and people need to be noob! thx in advanced

Akrem Hadji on 17 Oct 2020

Please add a precision threshold for floating numbers. Sometimes I get results with an error ~ e-17 close, but still not accepted.

Anton Casas on 2 Nov 2020

Test cases with 2 input arguments can be very tricky for people without knowledge of nargin, and that is off-topic here. I think a hint should be added on the problem description.

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Problem 972. Set a diagonal

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Problem 972. Set a diagonal

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