I am running a script in Matlab R2020b. The script contains an array with following values:

a=[500, 500, 500, 1000, 750, 750, 567.79 613.04]

The script as an equation:

(a(1)*(a(8)-a(6)) a(7)*(a(6)-a(2)) a(5)*(a(2)-a(8)))

When running on Matlab the above equation gives the answer -11312 for the values of array a. But when I calculate each value separately and add them the Matlab compiler gives a different answer.

a(1)*(a(8)-a(6)) = -68480
a(7)*(a(6)-a(2)) = 1.419e 05
a(5)*(a(2)-a(8)) = -84780
>>(-68480)   (1.419e 05)  (-84780) 

the answer for the above is -11310.

A screenshot of the commands is also attached.

kindly tell me why Matlab compiler gives these different answers??

CodePudding user response：

The problem is that MATLAB's default format is 'short', and this is not showing you complete precision. Try format long.

>> format long
>> a(7)*(a(6)-a(2))
ans =
     1.419475000000000e 05

CodePudding user response：

You are wrong.

If you add format long g you can see the real numbers:

format long g

a=[500, 500, 500, 1000, 750, 750, 567.79 613.04]
res1=(a(1)*(a(8)-a(6))   a(7)*(a(6)-a(2))  a(5)*(a(2)-a(8)))
a2=a(7)*(a(6)-a(2))
a1=a(1)*(a(8)-a(6))
a3=a(5)*(a(2)-a(8))
res2=a1 a2 a3

results in:

res1 =

                  -11312.5


a2 =

                  141947.5


a1 =

                    -68480


a3 =

                    -84780


res2 =

                  -11312.5