Find Function gives empty matrix

a=0:0.1:90;

V=find(a==3.4);

so when i type in the above code, it should give me the indice of where a=3.4, but instead, V is an empty matrix.

but if i try to find V=find(a==3.5), it works well...

i know this may due to tolerance and accuracy stuffs...but is there a quick way to fix this ?

Thank you for your help!

Answer 1

[Azzi Abdelmalek]

a=0:0.1:90
V=find(a==0.1*34)

[Jay]

Thank you ! but could you please tell me how come it worked for 3.5 but not for 3.4?

[Azzi Abdelmalek]

0.1 and 3.4 are saved in memory with a certain precision, it's not obvious that 0.1*34 and 3.4 will be exactly equal. try:

3.4-0.1*34

It happens that they are equal

3.5==0.1*35

[Jay]

thank you !

[Azzi Abdelmalek]

You can also use

tol=0.00001  
V=find(abs(a-3.4)<tol)