MATLAB: How to define the own signum function

signum

Hello all,
I am trying to better my programming skills with MATLAB. I wanted to see if I could create my own set of instructions that perform exactly like the signum function does. For example,
    X = [-3 0 4];
    Y = sign(X)
    Y = 
        -1    0    1
Your answer gets put in an array.
I tried doing this by using if constructs. I only got it to work when the user puts in a single number. Here's my work:
    prompt = 'Give a number: ';
    result = input(prompt);
    X = result;
    if X < 0
        Y = -1
    elseif X == 0 
        Y = 0
    else 
        Y = 1
    end
I don't know how to have someone input an array (like [-3 0 4] ). I also don't know how to have my answer display as an array. Could someone help?

Best Answer

Anthony, looking good. Put the code into a function and use inputdlg to allow inputting the numbers more easily. Alternatively, you could simply let the user define the matrix X and use it as an input for the function.
 function Y = my_sig()
 prompt = {'Input dialog'};
 name   = 'Input dialog';
 Xcell  = inputdlg(prompt, name);
 X      = str2num(Xcell{1});
 Y      = zeros(size(X));
 for ii = 1:numel(X)    % loop through all elements of the vector
    if X(ii) < 0
        Y(ii) = -1;
    elseif X(ii) == 0
        Y(ii) = 0;
    else
        Y(ii) = 1;
    end
 end
 end
Related Question