Why are symbolic expressions being rounded?

I'm deriving some expressions symbolically and then substituting values and computing the results and I only recently noticed that the results are being rounded.

>> format long
>> syms x; double(subs(10/x,x,3))

ans =

   3.333300000000000
   

or simply,

>> x = sym(3.33333333)
 
x =
 
3.3333
 
>> double(x)

ans =

   3.333300000000000

I can't even reproduce results from the documentation it seems:

>> syms x
>> p = sym(pi);
>> piVpa = vpa(p)
 
piVpa =
 
3.1416
 

According to the documentation, this is supposed to produce:

piVpa =

3.1415926535897932384626433832795

[Bill Tubbs]

Actually, I think it is double that is doing the rounding:

>> syms x; 10/3 - subs(10/x,x,3)
 
ans =
 
0
 
>> 10/3 - double(subs(10/x,x,3))

ans =

     3.333333333355171e-05

Answer 1

[Bill Tubbs]

Mathworks technical support have diagnosed the problem. Don't know what caused it originally but the 'FloatingPointOutput' setting in the symbolic preferences was set to 1.

Here is the solution to fix it:

>> sympref

ans = 

  struct with fields:

           FourierParameters: [1×2 sym]
           HeavisideAtOrigin: [1×1 sym]
            AbbreviateOutput: 1
               TypesetOutput: 1
         FloatingPointOutput: 1
      PolynomialDisplayStyle: 'default'
    MatrixWithSquareBrackets: 0

>> sympref('FloatingPointOutput','default');
>> double(sym('pi'))

ans =

   3.141592653589793

>> p = sym(pi);
>> piVpa = vpa(p)
 
piVpa =
 
3.1415926535897932384626433832795
 

Answer 2

[Steven Lord]

Have you changed your digits setting?

help digits

Are you calling the correct double function? What does this show?

which double(x)

[Bill Tubbs]

Digits = 32

which double(x)

returns

/Applications/MATLAB_R2019b.app/toolbox/symbolic/symbolic/@sym/sym.m % sym method