I have a function file, I want to input an array and evaluate each cell in that array. How do I alter my function file to do this?

function x=isoddm(a)

if isnan(a)==1

      x=-1;
  elseif mod(a,2)==0.5
      x=-1;
  elseif mod(a,2)==1.5
      x=-1;
  elseif mod(a,2)==0
      x=0;
  elseif mod(a,2)==1
      x=1;
  else
      x=nan;
  end

The purpose of this function is to see whether an array element is an integer or not and if it is, is it an even or odd number. The problem I am having is that it cannot evaluate each cell in an array individually.

[Walter Roberson]

Duplicates http://www.mathworks.co.uk/matlabcentral/answers/70397

Answer 1

[Marco]

I have found a long and painful answer to my own question that does not involve WR's suggestion. I remade x into x1, x2, and x3. Here is the nested if loop for x1, which determines if a(1) is a real number then proceeds to determine if it is nan or not, then an integer, then even or odd;

function [x1,x2,x3]=isoddm3(a)
% For x1
if isreal(a(1))==0
    x1=-1;
elseif isreal(a(1))==1
    if isnan(a(1))==1
        x1=-1;
    elseif mod(a(1),2)==0.5cle
        x1=-1;
    elseif mod(a(1),2)==1.5
        x1=-1;
    elseif mod(a(1),2)==0
        x1=0;
    elseif mod(a(1),2)==1
        x1=1;
    end
end

It goes on to calculate x2 and x3, which are exactly the same steps for x1 but replaced with x2 or x3. At the end I had to produce a psuedo-array for x using fprintf; fprintf('x=[%g\n %g\n\n %g\n\n\n] Ignore ans',x1,x2,x3) because the answer (ans) would only display x1.

[Marco]

on the line elseif mod(a(1),2)==0.5cle get rid of the clear, its a mistake

Answer 2

[Walter Roberson]

Use logical indexing. For example,

x = -1 * ones(size(a));
x( mod(a,b) == c ) = d;

[Marco]

Are you suggesting that I do this for each statement line in the if loop?

[Marco]

I'm not sure what you mean, and I've tried your first suggestion but it resulted in NaN NaN NaN, not the answer I expect for the first two elements, and I'm confused by the second, what do b and c represent?

[Walter Roberson]

There is no such thing as an "if loop". There are "for loop" and "while loop" and "if statement". The body of an "if" executes either 0 times (for false) or 1 time (for true); loops are for executing the body multiple times.

In my example, b, c, and d are values you will need to determine for your purposes. For example in one case, "b" might be 2. I deliberately did not give examples of what values you would use for b, c, and d because most of your original code was wrong (and still is, in your code that you Accepted.)

You basically have 3 cases: one case is all the situations that produce -1, one case is the situations that produce 0, and one case is the situations that produce 1. Your series of "if" statements can be replaced by an initialization of x, followed by three statements of the form

x( mod(a,b) == c ) = d;

with appropriately chosen "b", "c", and "d" (e.g., in one case, d would be -1, in another it would be 0, in the third it would be 1.)

To give an example, if you were required to give -3 for numbers of the form of 7x+5, then

x( mod(a, 7) == 5 ) = -3;