Doug’s MATLAB Video Tutorials

December 1st, 2008

if (answer == 1)
     Do something
end

if abs(answer - 1) < 1e-14
     Do something
end


       
       
              

                     


                     
              
              
 






By 
Doug Hull









21:43 UTC | 
Posted in Format: Video,  Level: Advanced |
Permalink |



	
				

					
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4 Responses to “Video tutorial: Tolerances in comparisons”
 

	


	
		

			
			paramesh replied on
December 2nd, 2008 at 16:49 UTC :
			


			
Hi Doug,
Nice point. But instead, won’t the function “round” work? Say, “if round(answer) == 1″.




		

	
	
		

			
			matt fig replied on
December 2nd, 2008 at 18:13 UTC :
			


			
paramesh,
Your solution will work if the integer is known, as it is in this case (1).  However Doug’s solution is more general in that it can be applied to determine if an integer is present when the integer may be unknown.  As in:
abs(round(N) - N)<tol
Where N can be an array of possible integers which resulted from a previous calculation.  This will be true when integers are found in N and false where not.




		

	
	
		

			
			Seth Popinchalk replied on
December 6th, 2008 at 14:58 UTC :
			


			
@paramesh - I don’t like the ROUND solution at all.  That would return true for 1.4 and .6!  As matt fig points out, you need to set a tolerance bound on your comparison.




		

	
	
		

			
			Leonardo Glavina replied on
April 23rd, 2009 at 12:20 UTC :
			


			
That’s true Seth, but you can use a type of trick to make it more precise, like [i]round(100*w)/100[/i] or even [i]round(1000*w)/1000[/i].
Anyway, great solution Doug… I was having a little bit of problem with that, when I was making comparisons to find the intersection points of plots, and this method can be better than mine.




		

	
	
	

 


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