I have a 17658x1 double matrix. I want to find the values of indices when matrix elements are equal to k(here .1).

I have a 17658x1 double matrix. I want to find the values of indices when matrix elements are equal to k(here .1).

Answer 1

[Birdman]

For instance, imagine you want to find 1 in a randomly generated matrix:

A=randi([1 5],17658,1);&demo data
idx=find(A==1);

[Stephen23]

@Birdman: the user is asking about how to test for equality of floating point numbers (e.g. 0.1). This topic come up so often that I am sure you would not recommend testing for equality:

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

https://www.mathworks.com/matlabcentral/answers/57444-faq-why-is-0-3-0-2-0-1-not-equal-to-zero

https://www.mathworks.com/matlabcentral/answers/69-why-does-1-2-3-1-3-not-equal-zero#answer_271

https://www.mathworks.com/matlabcentral/answers/316889-why-two-equal-numbers-are-not-equal

https://www.mathworks.com/matlabcentral/answers/41536-why-is-2-24-10-22-4-not-equal-to-0

https://www.mathworks.com/matlabcentral/answers/20830-1-0010-does-not-equal-1-0010

etc, etc, etc

Always use a tolerance when comparing floating point values.

[Birdman]

Oh yes I did not read that carefully. Then, ismembertol should do it.

https://www.mathworks.com/help/matlab/ref/ismembertol.html

[Abhishek Maurya]

Thankyou so much. idx=find(A==k); is working properly for floating numbers too, unless the exact value of the number is known like k=3.051757812500000e-05. Thankyou Birdman,Stephen Cobeldick.