How to tell when you have a precision problem, an equality problem, or a MATLAB bug

I am using an educational version of MATLAB R2012a on a Mac running OS X 10.8.5.

I am having issues with equality of two different numbers. When I expand the displayed precision the numbers are exactly the same, so why is my equality failing?

EDU>> deltaArray(3,2)

ans =

      0.0951

EDU>> deltaArray(3,2) == d_t

ans =

       0

EDU>> d_t

d_t =

      0.0951

EDU>> format 'long'
EDU>> d_t

d_t =

     0.095145024596147

EDU>> deltaArray(3,2)

ans =

     0.095145024596147

Answer 1

[Walter Roberson]

format long still does not show all of the digits. Try

sprintf('%.30g - %.30g = %.30g', deltaArray(3,2), d_t, deltaArray(3,2) - d_t)

[Joel]

Thank you!

sprintf('%.30g - %.30g = %.30g', deltaArray(3,2), d_t, deltaArray(3,2) - d_t)

ans =

0.0951450245961471680056220634469 - 0.0951450245961471263722586400036 = 4.16333634234433702658861875534e-17