How to assign values to a MATLAB matrix on the diagonal?

by

I usually use EYE for that:

A = magic(4)
A(logical(eye(size(A)))) = 99

A =
    99     2     3    13
     5    99    10     8
     9     7    99    12
     4    14    15    99

Alternatively, you can just create the list of linear indices, since from one diagonal element to the next, it takes nRows+1 steps:

[nRows,nCols] = size(A);
A(1:(nRows+1):nRows*nCols) = 101
A =
   101     2     3    13
     5   101    10     8
     9     7   101    12
     4    14    15   101

If you only want to access a subset of diagonal elements, you need to create a list of diagonal indices:

subsetIdx = [1 3];
diagonalIdx = (subsetIdx-1) * (nRows + 1) + 1;
A(diagonalIdx) = 203
A =
   203     2     3    13
     5   101    10     8
     9     7   203    12
     4    14    15   101

Alternatively, you can create a logical index array using diag (works only for square arrays)

diagonalIdx = false(nRows,1);
diagonalIdx(subsetIdx) = true;
A(diag(diagonalIdx)) = -1
A =
    -1     2     3    13
     5   101    10     8
     9     7    -1    12
     4    14    15   101

More Related Contents:

  1. Is vectorised data manipulation sequential (e.g R and MATLAB)?
  2. Finding islands of zeros in a sequence
  3. Create a zero-filled 2D array with ones at positions indexed by a vector
  4. How can I apply a function to every row/column of a matrix in MATLAB?
  5. Multiply a 3D matrix with a 2D matrix
  6. pdist2 equivalent in MATLAB version 7
  7. Vectorizing the Notion of Colon (:) – values between two vectors in MATLAB
  8. How do I compare all elements of two arrays?
  9. Fast Algorithms for Finding Pairwise Euclidean Distance (Distance Matrix)
  10. BSXFUN on memory efficiency with relational operations
  11. MATLAB: Subtracting matrix subsets by specific rows
  12. Efficiently compute a 3D matrix of outer products – MATLAB
  13. how to get a single feature vector from SIFT descriptor [closed]
  14. Generate random number with given probability matlab
  15. Matlab: Running an m-file from command-line
  16. Use a vector as an index to a matrix
  17. How to concatenate a number to a variable name in MATLAB?
  18. Matlab – PCA analysis and reconstruction of multi dimensional data
  19. Why is reshape so fast? (Spoiler: Copy-on-Write)
  20. MATLAB: Is it possible to have two event values whilst using ode45?
  21. MATLAB: Is it possible to overload operators on native constructs (cells, structs, etc)?
  22. What are some efficient ways to combine two structures in MATLAB?
  23. Difference of handle and values classes
  24. MATLAB: Differences between .mat versions
  25. In Matlab, is it possible to terminate a script, but save all its internal variables to workspace?
  26. How to change an image from Cartesian to Polar coordinates in Matlab?
  27. MatLab error: cannot open with static TLS
  28. Iterating through struct fieldnames in MATLAB
  29. Using OpenGL in Matlab to get depth buffer
  30. MATLAB linked list

Leave a Comment