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MATLAB, separate odds and evens from matrix

  1. Jan 29, 2015 #1

    Feodalherren

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    1. The problem statement, all variables and given/known data

    Given variable b that contains a row vector of length 10, assign the contents of the odd indeces in b to variable odd , and assign the contents of the even indeces of b to variable even.

    Examples:

    Input b = [8 -3 0 7 -6 -3 1 8 7 -2]
    Output odd = [8 0 -6 1 7]
    even =[-3 7 -3 8 -2]


    2. Relevant equations


    3. The attempt at a solution

    b is some arbitrary matrix




    O = mod(b,2);
    odd = b(O)


    E = ~mod(b,2);
    even = b(E)

    What's weird is that it works for b(E) but b(O) yields and error: Subscript indices must either be real positive integers or logicals.
     
    Feodalherren, Jan 29, 2015
  2. jcsd
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  3. Jan 29, 2015 #2

    RUber

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    Homework Helper

    I am not sure that mod is the best command to use for this purpose. You are just looking to split the matrix into 2 parts based on whether or not the index is odd or ever, right?
    You essentially want something that looks like:
    b = [8 -3 0 7 -6 -3 1 8 7 -2];
    O=[1,3,5,7,9];
    E=[2,4,6,8,10];
    odd = b(O)
    even=b(E)
    The mod function was returning a logical index of whether or not the value was odd or even.
     
    RUber, Jan 29, 2015
  4. Jan 29, 2015 #3

    Feodalherren

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    But it has to be true for any arbitrary matrix of any length of numbers :/.
     
    Feodalherren, Jan 29, 2015
  5. Jan 30, 2015 #4

    milesyoung

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    You want to generate the sequences 1,3,5,... and 2,4,6,... to use as indices for your matrix. Do you know of any easy way to do that in MATLAB? Hint: The colon operator.
     
    milesyoung, Jan 30, 2015
  6. Jan 30, 2015 #5

    RUber

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    Homework Helper

    For arbitrary length arrays, you can call length(b) to get your ending value. Or as milesyoung said, it might be more straightforward to use odd = b([1:2:end]) to count by twos using the colon.
     
    RUber, Jan 30, 2015
  7. Jan 30, 2015 #6

    Feodalherren

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    Ah ok, got it. Thanks!
     
    Feodalherren, Jan 30, 2015
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