Why some lements are not found using find in matlab array

I used following code

a=0:0.001:3
ismember(2.8,a)

ans=1

later I changed

a=0:0.001:3
ismember(2.8,a)

ans=0

I then checked the element present at

a(2801)

ans=2.80000

then why ismemeber is not showing the element found in array when it actually exists?

Answer 1

[Walter Roberson]

http://matlab.wikia.com/wiki/FAQ#Why_is_0.3_-_0.2_-_0.1_.28or_similar.29_not_equal_to_zero.3F

[Satish Salunkhe]

I used following code

a=0:0.001:3 ismember(2.8,a)

ans=1

later I changed

a=0:0.001:10 ismember(2.8,a)

ans=0

I then checked the element present at

a(2801)

ans=2.80000

then why ismemeber is not showing the element found in array when it actually exists?

I want to use following code, a=0:0.001:10 b=trimf(a,[2.8 2.8 2.8]) plot(a,b)

except 2.8 rest x values are having y axis value 0. But I am getting all values zeros. can you please help me to reach the goal?

[Satish Salunkhe]

However when you are dealing with floating point numbers, or just want to have close matches (+- 1000 is also possible), the best solution I found is the fairly efficient File Exchange Submission: ismemberf http://www.mathworks.com/matlabcentral/fileexchange/23294-ismemberf

It gives a very practical example:

[tf, loc]=ismember(0.3, 0:0.1:1) % returns false [tf, loc]=ismemberf(0.3, 0:0.1:1) % returns true

Though the default tolerance should normally be sufficient, it gives you more flexibility

ismemberf(9.99, 0:10:100) % returns false ismemberf(9.99, 0:10:100,'tol',0.05) % returns true

I think I resolved problem somewhat