cannot find existing number

I have the following data where fs =100;

tstamp =(1/fs:1/fs:12000*(1/fs))

Then when looking for the value 117 (find(tstamp == 117)), the results is [], however, the value does exist though with a trail of zeros (117.0000), is that the prob? how to solve?

Please help with this very likely simple prob.

cheers

Eduardo

Answer 1

[Star Strider]

See the documentation section on Floating-Point Numbers for a full explanation.

Actually, I can’t reproduce that exact problem, since it works correctly here —

format long

fs =100;
tstamp =(1/fs:1/fs:12000*(1/fs))

tstamp = 1×12000

0.010000000000000 0.020000000000000 0.030000000000000 0.040000000000000 0.050000000000000 0.060000000000000 0.070000000000000 0.080000000000000 0.090000000000000 0.100000000000000 0.110000000000000 0.120000000000000 0.130000000000000 0.140000000000000 0.150000000000000 0.160000000000000 0.170000000000000 0.180000000000000 0.190000000000000 0.200000000000000 0.210000000000000 0.220000000000000 0.230000000000000 0.240000000000000 0.250000000000000 0.260000000000000 0.270000000000000 0.280000000000000 0.290000000000000 0.300000000000000

v = find(tstamp == 117)

v = 
       11700

D = v - 11700

D = 
     0

I was hoping to be able to demonstrate floating-point approximation error.

Oh well ...

.

[Luis Eduardo Cofré Lizama]

Many thanks for the link. Fro some reason, I qshut and open again Matalab and the prob is gone?... odd

[Walter Roberson]

There are various fairly obscure ways in which the floating point round-off algorithm can end up being changed. That does not happen often, but it can happen.

[Star Strider]

@Luis Eduardo Cofré Lizama — As always, my pleasure!

Answer 2

[Walter Roberson]

See the discussion at https://www.mathworks.com/matlabcentral/answers/1889267-wrong-output-using-find-while-filtering-a-matrix#answer_1142502