You got confused by the different ways C++ and MATLAB are printing double values. MATLAB’s format long
only prints 15 significant digits while C++ prints 17 significant digits. Internally both use the same numbers: IEEE 754 64 bit floating point numbers. To reproduce the C++-behaviour in MATLAB, I defined a anonymous function disp17
which prints numbers with 17 significant digits:
>> disp17=@(x)(disp(num2str(x,17)))
disp17 =
@(x)(disp(num2str(x,17)))
>> 1.0 / 1.45
ans =
0.689655172413793
>> disp17(1.0 / 1.45)
0.68965517241379315
You see the result in MATLAB and C++ is the same, they just print a different number of digits. If you now continue in both programming languages with the same constant, you get the same result.
>> D = 0.68965517241379315 %17 digits, enough to represent a double.
D =
0.689655172413793
>> ans = 2600 / D %Result looks wrong
ans =
3.770000000000000e+03
>> disp17(2600 / D) %But displaying 17 digits it is the same.
3769.9999999999995
The background for printing 17 or 15 digits:
- A double requires 17 significant digits to be stored without precision loss, which is what C prints.
- For up to 15 digits any number can be converted from string to double to string and results back in the original number, which is what MATLAB does.