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From: Bayo on 12 Mar 2010 19:17
Hi
Does anyone know if there's a function in matlab that compares the sign of two values? i.e it checks if they are both negative or positive?


Bayo
From: John D'Errico on 12 Mar 2010 19:27
"Bayo " <ayb503(a)bham.ac.uk> wrote in message <hnelim$36s$1(a)fred.mathworks.com>...
> Hi
> Does anyone know if there's a function in matlab that compares the sign of two values? i.e it checks if they are both negative or positive?
>

No. There is no such explicit function.

However, suppose you take the product of the two
numbers?

What happens if both of them are positive? What
if they are both negative?

John
From: Walter Roberson on 12 Mar 2010 19:27
Bayo wrote:

> Does anyone know if there's a function in matlab that compares the sign
> of two values? i.e it checks if they are both negative or positive?

x and y have the same sign if

sign(x)*sign(y) > 0

This has been constructed to return false if either or both numbers are 0, on
the grounds that 0 has no sign. If you wish two 0's to be considered to have
the same sign, then use

sign(x) == sign(y)


If you wish to consider two numbers to have the same sign if either of them is
0 or they both have the same sign (that is, that 0 is considered to belong to
both sides), then use

sign(x) * sign(y) > -1
From: Nathan on 12 Mar 2010 19:41
On Mar 12, 4:17 pm, "Bayo " <ayb...(a)bham.ac.uk> wrote:
> Hi
> Does anyone know if there's a function in matlab that compares the sign of two values? i.e it checks if they are both negative or positive?
>
> Bayo

You can easily create one with outputs depending on what you are
looking for:

function pol = polfunc(a,b)
%POLFUNC determines the polarity of two numbers
% Inputs: two numbers, a and b
% pol returns 0 if number have opposite signs
% pol returns 1 if numbers are both negative
% pol returns 2 if numbers are both positive
signbool = a>0;
if (a*b)>0
pol = signbool+1
else
pol = 0;
end
end

-Nathan
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