format long addition problem

with format long

7.5e-6+1e-7

ans =

       7.600000000000000e-06

>> 7.6e-6+1e-7

ans =

       7.700000000000001e-06

**why not 7.6e-6+1e-7

ans = 7.700000000000000e-06**

and how can i avoid this 0.000000000000001e-06???

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

[AR]

how can i convert 7.700000000000001e-06 to 7.7e-06????

[Walter Roberson]

You can use the symbolic toolbox, or you can use the fixed-point toolbox, or you can write your own Class for decimal arithmetic, or you can use a totally different tool that already implements decimal arithmetic.

There is no exact representation for 7.7e-06 in IEEE 754 binary floating point such as is used by MATLAB (and which is an international standard for numeric representation.) The closest you can get is

7.70000000000000081623076353398715809817076660692691802978515625e-06