Homework Help: MATLAB, separate odds and evens from matrix

Feodalherren · Jan 29, 2015

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.

RUber · Jan 29, 2015

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.

Feodalherren · Jan 29, 2015

But it has to be true for any arbitrary matrix of any length of numbers :/.

milesyoung · Jan 30, 2015

Feodalherren said: ↑

But it has to be true for any arbitrary matrix of any length of numbers :/.

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.

RUber · Jan 30, 2015

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.

Feodalherren · Jan 30, 2015

Ah ok, got it. Thanks!