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Need to fill a triangular matrix on MATLAB with the ndgrid command without using loops.
$\mathbf{Example:}$ To fill a square matrix $a_{ij} = i+2j$, for $i,j = 1..10$, the code would be :
[I,J] = ndgrid(1:10,1:10); A = I+2.*J;
But I don't know how to do so if my matrix is triangular. Say, the matrix defined by :
$a_{ij} = i+2j \quad$, if $i \le j$ and
$a_{ij} = 0 \quad\quad\quad$, if $i > j$
1 Answer
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Try [I,J] = ndgrid(1:10,1:10); A = I+2.*J; A(I > J) = 0;
The last line creates a boolean mask which is true for the indices where $i > j$, and then zeroes out those entries of $A$.
