About isinteger command(confusion)

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C Zeng
C Zeng 2013-3-14
编辑： per isakson 2015-1-16
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?

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per isakson
per isakson 2013-3-14
编辑：per isakson 2015-1-16
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.)
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Jan
Jan 2013-3-16
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 2013-3-17
Thanks, I understand it. It is good to know.

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更多回答（2 个）

Jan
Jan 2013-3-16
Joining the rounding with the checks for overflows:
function isf = isflint(m)
isf = (abs(m) <= bitmax && m == floor(m));
ChristianW
ChristianW 2013-3-14
doc isinteger
isinteger(int8(3))
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Jan
Jan 2013-3-16
@C Zeng: @(x) x==round(x) is an anonymous function. You find an exhaustive description ion the documentation.

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