MATLAB: How to replace the zeros in a matrix with another integer, or with a pos or neg infinity

2ddistancematrixmatrix manipulationreplace

I have a 145×145 distance matrix where: (1,1)=0 (2,2)=0 … Can I replace just the diagonal with infinity values? There are other zeros in the matrix, but I may or may not want to keep those. Is there a process that could replace this diagonal of all zeros with a diagonal of all infinities?

thanx

Best Answer

To replace only the diagonal of a N-by-N matrix with infinity, do:

A(1:N+1:N^2) = inf;  % or A(1:N+1:end)...

If you want to replace all of the zeros in an array with infinity, do:

A(~A) = inf;  % Or A(A==0) = inf;

Related Solutions

MATLAB: Start every iteration of for loop with same matrix

Simply make a copy inside the loop, and work on the copy only:

for n = 1:length(x)
    y = x;
    y(:,n) = Inf;
    y(n,s) = Inf;
    [reduced_node_matrix,cost] = reduction(y);
end

Note that the output from length changes depending on the size of the inputs. If you want to write reliable code then you should always use size or numel instead of length.

MATLAB: Realmax + 1 infinity

Because the value 1 is nowhere near the smallest value that can be added to realmax to create a new value. You would need to add a value that is more than half the difference between representable values around the magnitude of realmax. To get that value try using eps:

>> val = eps(realmax) % much bigger than 1.
val = 1.9958e+292
>> realmax + val/2
ans = Inf
>> realmax + val/3
ans = 1.7977e+308

This is exactly the same as if you add 1e-300 to 10: the answer is 10, because 1e-300 is nowhere near the difference in representable values around the magnitude 10, so adding 1e-300 makes absolutely no difference to the 10.

Best Answer

Related Solutions

MATLAB: Start every iteration of for loop with same matrix

MATLAB: Realmax + 1 infinity

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