How to make a variable negative if another variable is negative?

I have two columns (X & Y) full of numbers 200 numbers in a text file.

All values of X are positive, while the values of Y are mixed with negative and positive numbers.

I'm trying to create a simple if statement, so change all of the X values that correspond to a negative Y value, to negative.

This code does not work though:

Code:

if Y < 0
X1 = X*(-1)
end

Unrecognized function or variable 'Y'.

[Andrew Lackey]

Thank you!

Answer 1

[Matt J]

X1=X.*sign(Y);