ifelse and switch don't match

Hi, my problem is this code:

if A21 == N2

Re21 = N2r;

elseif A21 == I2

Re21 = I2r;

elseif A21 == R2

Re21 = R2r;

elseif A21 == T2

Re21 = T2r;

end

I2 and R2 have the same value so, when I put A21 = R2, the value of Re21 is I2r because MATLAB thinks that I2 and R2 are the same variable, It only took the first value in the code (I2). I need that MATLAB recognize that Re21 is R2r. How can I fix it? Same isue with Switch.

[DGM]

MATLAB doesn't think I2 and R2 are the same variable. If A21 == R2, and R2 == I2, then A21 == I2. The second case matches, and that's it. The only assignment that is performed is Re21 = I2r.

if A21 == N2
    Re21 = N2r;
elseif A21 == I2 % this is true
    Re21 = I2r;
elseif A21 == R2 % this is also true, but it's never used if the prior case is true
    Re21 = R2r;
elseif A21 == T2
    Re21 = T2r;
end

That's how if-elseif conditionals work.

If R2r and I2r are unique values, then how do you propose to have a variable that is simultaneously equal to two different things? If instead they're identical values, then what's the difference?

[Ignacio Brown Vidal]

I see, the problem is that I2 and R2 are input data for two diferents lines of transmission that have the same value. I think that I will have to use simbolic variable (syms) for them. Thanks. (sorry for my bad english).

[Steven Lord]

Can you tell us (in words not code) what the various variable represent and what decision or thought process the code you've posted is supposed to implement? Having a better understanding of the underlying problem you're trying to solve may help us offer alternate solutions that may avoid the edge cases or potential problems of the solution you posted.

[Ignacio Brown Vidal]

The R2, N2, T2 and I2 represents state of a line of electrical distribution system, A21 and Re21 are part of diferents matrix (6x6). So, deppending of the state, I put R2, N2 T2 or I2 until I complete the matrix. My error was that I put values for the states variables so, in case that two or more of the states have the same value, MATLAB will always match the first statement of the IF ELSEIF, in this case, Re21 = I2r, when I need the statemen Re21 = R2r. In order to make MATLAB use the statement I need, I make R2, N2, T2 and I2 symbolic variables, so when I put A21=R2, MATLAB will use the statement R21 = R2r.

Answer 1

[Steven Lord]

Based on your prose description, it sounds like your underlying task is to populate the matrix Re21 based on the contents of the matrix A21. Is that correct? If so you could consider either logical indexing or the discretize function depending on whether the states in A21 are discrete or continuous.

A21 = randi(10, 5, 5) % Sample data

A21 = 5×5

3 8 2 4 8 6 9 5 1 7 3 1 7 4 8 9 1 5 6 5 7 8 8 2 1

Re21 = zeros(size(A21)) % Sample target

Re21 = 5×5

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

Re21(A21 == 1) = 11

Re21 = 5×5

0 0 0 0 0 0 0 0 11 0 0 11 0 0 0 0 11 0 0 0 0 0 0 0 11

Re21(A21 == 3) = 333

Re21 = 5×5

333 0 0 0 0 0 0 0 11 0 333 11 0 0 0 0 11 0 0 0 0 0 0 0 11

Re21(A21 == 7) = NaN

Re21 = 5×5

333 0 0 0 0 0 0 0 11 NaN 333 11 NaN 0 0 0 11 0 0 0 NaN 0 0 0 11

Re21(A21 == 9) = -1

Re21 = 5×5

333 0 0 0 0 0 -1 0 11 NaN 333 11 NaN 0 0 -1 11 0 0 0 NaN 0 0 0 11

Or for the continuous case, where values in A21 in the range [0, 3) should become -1 in Re21, values in [3, 7) should become 2, values in [7, 8) should become -33, and values in [8, 10] should become 444:

A21 % Display for reference

A21 = 5×5

3 8 2 4 8 6 9 5 1 7 3 1 7 4 8 9 1 5 6 5 7 8 8 2 1

Re21_2 = discretize(A21, [0 3 7 8 10], [-1, 2, -33, 444])

Re21_2 = 5×5

2 444 -1 2 444 2 444 2 -1 -33 2 -1 -33 2 444 444 -1 2 2 2 -33 444 444 -1 -1

Now neither of these would make elements in Re21 take on two different values if the value in an element of A21 matches two of your conditions. As a concrete example if you wanted Re21 to be 1 if the value in A21 was in the range [3, 6) and 2 if it was in the range [4, 7) then you have to choose if it should be 1 or 2 if the value in A21 is 5. It can't be both. [Those overlapping ranges might also be a code smell.]

[Ignacio Brown Vidal]

Thanks!!