MATLAB: Is it possible to combine “for” and “if” like this

matrix manipulation

Hello, Iam new at computing and matlab, I have a problem with the next part of my program.
nodos = [0     0     0     0     1     1; 48     0     0     0     1     1;84     0     0     0     1     1;48    36  -500     0     0     0]
Nnodos=4
for i=1:Nnodos
w=0
   if nodos(i,5)==0    
   nodos(i,7)=w+1
   w=w+1
  
   end
end
When i run the program the matrix "nodos" is not modified. Is the i going from 1 to Nnodos?
thanks for your time.

Best Answer

Rachuan - when I run the code, the matrix nodos is modified. In fact, a seventh column is appended to the original 4x6 matrix. Look at the condition that when true, updates the matrix
 if nodos(i,5)==0    
   nodos(i,7)=w+1
   w=w+1  
 end
So if the fifth element of the ith row is zero, then you set the seventh element of the ith row to w+1. But since your matrix is 4x6, a seventh column of zeros is automatically added to the matrix with only nodos(i,7) equal to one. The code then increments w and proceeds to the next iteration of the loop. But the first line of the for loop body
 w=0
So even though we have incremented w, we have reset it to zero. I suspect that you only want to initialize w to zero outside of the for loop. So you may want to revise your code as
 nodos = [0 0 0 0 1 1; 48 0 0 0 1 1;84 0 0 0 1 1;48 36 -500 0 0 0]
 Nnodos = 4;
 w      = 0;
 for i=1:Nnodos
    if nodos(i,5)==0    
        nodos(i,7)=w+1;
        w=w+1;
    end
 end
Now decide what should happen when nodos(i,5)==0 0 do you want to add a new column, or update an existing one with nodos(i,??)=w+1;
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