我能像 matlab 一样在 python 中得到完全相同的总和 output

Question

i am converting a matlab code to python. i found a strange difference of sum of matlab and python. i want to have same output in python like i am getting in matlab. is it possible? in matlab

 x = [-200:200]/200; % 401 values from -200 to 200 y =sum(x) y = 9.9920e-16

but in python using different modules i get answer

x = np.arange(-200,201)/200 # 401 values from -200 to 200 y = np.sum(x) y = 1.4210854715202004e-14 z = sum(x) z = -8.43769498715119e-15 zmath = math.fsum(x) zmath = 0.0

Answer 1

The difference is not the numeric representation but in the order of summation. You can see this just in Matlab:

>> sum(x(randperm(401)))
ans =
   2.7756e-16
>> sum(x(randperm(401)))
ans =
   5.8842e-15
>> sum(x(randperm(401)))
ans =
  -2.2204e-15

The order of summation is going to depend on implementation details, eg, whether the array operation takes advantage of your CPU's vector registers. If you must have exactly the same result, you'll have to write an explicit loop. (Based on the answers you got, z = sum(x) in Python is doing that internally.) For more understanding of why this happens, see Why does changing the sum order returns a different result?