Comments on: When is a Numeric Result Not a Number?

By: Steve L

Steve L — Mon, 10 Jan 2011 19:06:22 +0000

Any relational operation involving NaN except for NE (not equals, or ~=) returns false. This is documented on the reference page for the NAN function:

http://www.mathworks.com/help/techdoc/ref/nan.html

So all of these return false:

NaN == 0
NaN > 0
NaN >= 0
NaN < 0
NaN <= 0

Only this returns true:

NaN ~= 0

By: Maxx

Maxx — Sat, 08 Jan 2011 06:50:35 +0000

In comparison NaN > 0 gives false. I think you should note about it.

An excellent article! Thank you!

By: Loren

Loren — Tue, 19 Jan 2010 20:37:50 +0000

OysterEngineer,

The class of NaN is double which is a numeric class. It’s not looking at values, but type.

–Loren

By: OysterEngineer

OysterEngineer — Tue, 19 Jan 2010 17:19:33 +0000

Please explain why a true is returned from:

isnumeric(NaN)

By: Loren

Loren — Thu, 19 Jun 2008 15:41:32 +0000

Gerrit-

Yes, ) * Inf should be 0.

Think about this. Anything times 0 is 0. But inf * anything is infinite. So with 2 answers possible (at least), how to choose? The answer is, don’t – return NaN. MATLAB can’t and doesn’t look at the overall expression you have and calculate limits. If you need special behavior for 0, code that into the algorithm.

–Loren

By: Gerrit

Gerrit — Thu, 19 Jun 2008 15:33:12 +0000

Should the result of inf * 0 really be NaN? Why? I have a term a .* (1 – (1 + b .* t) .* exp(-(b .* t))), 0

By: Steve

Steve — Fri, 04 Aug 2006 13:48:35 +0000

Even though the j doesn’t appear to have a real part, it does — it has a zero real part. That zero real part normally doesn’t make a difference in arithmetic operations, but it does when Inf and/or NaN are involved.

j*Inf = (0+1j)*(Inf+0j)
j*Inf = 0*Inf + 0*0j + 1j*Inf + 1j*0j
j*Inf = NaN + 0j + Inf*1j – 0
j*Inf = NaN + Inf*1j.

The case with Inf+j*Inf is as above, except you add Inf to NaN + Inf*1j to obtain NaN + Inf*1j.

Using COMPLEX as you mentioned is the way to obtain the number with 0 real part and Inf imaginary part, or Inf as both real and imaginary part. Using * does arithmetic; using COMPLEX does not.

By: Marcelo

Marcelo — Thu, 03 Aug 2006 23:38:56 +0000

Empty matrices, NaN and Inf are great, but fprintf, fscanf, sprintf and sscanf does not handle then consistently. Another inconsistent results are: j*Inf = NaN + j*Inf; Inf+j*Inf = NaN + j*Inf. My workarrounds for both then are complex(0,Inf) and complex(Inf,Inf).

By: per isakson

per isakson — Mon, 10 Jul 2006 17:01:09 +0000

I work with long time series of experimental data from heating and ventilation systems. I wish

MissingData to indicate that the data aquisition system was not working

NotDef to indicate that the quantity is not defined in the current mode of operation. E.g the inlet air temperature would be NotDef when the air handling unit it not operating.

I should probably include these two in my Time Series Object.

/ per

Please delete my previous reply. I guess the system swallowed “MissingData” and “NotDef”. / per

By: per isakson

per isakson — Mon, 10 Jul 2006 16:50:12 +0000

I work with long time series of experimental data from heating and ventilation systems. I wish

to indicate that the data aquisition system was not working

to indicate that the quantity is not defined in the current mode of operation. E.g the inlet air temperature is when the air handling unit it not operating.

I should probably include these two in my Time Series Object.

/ per