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About isinteger command(confusion)

Asked by C Zeng

C Zeng (view profile)

on 14 Mar 2013
Latest activity Edited by per isakson

per isakson (view profile)

on 16 Jan 2015

Hi, by the command of isinteger I can check if it is an integer, however, when defined at first, Matlab assume it is double precision right? So even a=3, isinteger(a) returns 0.

How to solve this problem?

0 Comments

C Zeng

C Zeng (view profile)

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3 Answers

Answer by per isakson

per isakson (view profile)

on 14 Mar 2013
Edited by per isakson

per isakson (view profile)

on 16 Jan 2015
Accepted answer

Matlab represents integers in differnt ways:

  • int8, int16, etc. see Christians answer
  • with a special use of double, which is called flint. See Floating Points

I use this function to test for flint

    function    isf = isflint( m )
    %   floating double only
        try
            bitand( abs( m ), 1 );
            isf = true;
        catch me
            isf = false;
        end
    end

I picked up the idea from a contribution by the "Pedestrian" in the FEX.

(I stripped off comments and error handling.)

5 Comments

C Zeng

C Zeng (view profile)

on 15 Mar 2013

Thanks, Isakson, will take a look.

Jan Simon

Jan Simon (view profile)

on 16 Mar 2013

The problem is to decide, if 1e17 is an integer or not: Because a double can store 16 digits only, this number does not contain any information about the fractional part for reasons of the precision. bitand() detect this and throw an error, while 1e17==round(1e17) replies true, because cropping the fractional part does not influence value.

C Zeng

C Zeng (view profile)

on 17 Mar 2013

Thanks, I understand it. It is good to know.

per isakson

per isakson (view profile)

Answer by Jan Simon

Jan Simon (view profile)

on 16 Mar 2013

Joining the rounding with the checks for overflows:

function isf = isflint(m)
isf = (abs(m) <= bitmax && m == floor(m)); 

1 Comment

per isakson

per isakson (view profile)

on 18 Mar 2013

I'll replace my cryptic isflint.

Jan Simon

Jan Simon (view profile)

Answer by ChristianW

ChristianW (view profile)

on 14 Mar 2013
doc isinteger
isinteger(int8(3))

5 Comments

C Zeng

C Zeng (view profile)

on 16 Mar 2013

yes, I used x==round(x) or floor(x). what do you mean by "isint = @(x)"?

Jan Simon

Jan Simon (view profile)

on 16 Mar 2013

@C Zeng: @(x) x==round(x) is an anonymous function. You find an exhaustive description ion the documentation.

C Zeng

C Zeng (view profile)

on 17 Mar 2013

OK

ChristianW

ChristianW (view profile)

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