Rounding off components of a matrix

Hello, I am new to matlab and I got stuck at a particular point.

I have a 256 x 904 matrix with entries between -1 and 1. I need to round it off in such a way that for entries less than or equal to 0, the output should be -1 and for entries greater than 0, the output should be 1.

So, I named this matrix X.

How do I denote X = (xij) in Matlab?

I was thinking of the following code:

if xij < = 0 xij= -1 else xij = 1 end

Could someone please help me?

Answer 1

[the cyclist]

This particular operation is easy to do across the entire matrix at once:

x = sign(x);

Even if there had not been a simple function that happened to do exactly what you needed, you can often do rounding operations cleverly on the whole matrix.

[Nusti]

Hi,

I don't understand how to write X(my 256 x 904 matrix) as (xij) (general representation of an element in ith row and jth column) in Matlab.

How does that work?

Then I can use that representation and write x = sign(x), I think.

[Walter Roberson]

X(i,j)

However, you do not need that representation for this purpose: sign(X) will do the entire matrix at once.

[Walter Roberson]

Note: sign(0) is 0, whereas Nusti requested -1 as the output for 0.

Answer 2

[Walter Roberson]

roundedX = (X > 0) * 2 - 1;

This will do the entire matrix at one time.

Another approach:

roundedX = ones(size(X));
roundedX(X <= 0) = -1;