vpa is not outputing enough digits

I'm having an error where vpa is only diplaying 5 digits when I need more. The code i have is:

syms x y
dx = 0.05

dx = 0.0500

f(x,y) = x*cos(x) + y
df = diff(f,x) + f*diff(f,y)
a = vpa(df(0,.5)/factorial(2)*dx^2)

a = 

0.001875

Obviosly here it outputs correctly to a = 0.001875, but on my end it outputs a = 0.0019. I've checked digits is set to the default 32 for vpa. The same thing occurs with

vpa(pi)

It outputs 3.1416 and not

vpa(pi)

ans = 

3.1415926535897932384626433832795

Answer 1

[John D'Errico]

I think you may have a setting messed up on your computer. For example...

X = sym(3)/32;
vpa(X)
ans =
0.09375

But now, if I try this:

sympref('floatingpointoutput',true);
vpa(X)
ans =
0.0938

Yet I have digits set as 32.

digits
Digits = 32

So you may want to reset sympref, as:

sympref('floatingpointoutput',false);

[Diego Mercado]

This was is! Thank you, don't know how that happened but gald its fixed.

Answer 2

[KSSV]

It seems a is a rational number so there are no digits to display else from zeros. Where as pi is a irrational number, so you have lot of digits to display.

For more discussion refer here: https://in.mathworks.com/matlabcentral/answers/320024-how-can-i-test-if-a-number-is-irrational

[Diego Mercado]

Ok, but there are more digits to display for a though. On my end, a = 0.0019 when it should be a = 0.001875. On my end vpa(pi) is rounding off after 5 digits where here it displays to many more digits.

[KSSV]

You can specify the number of digits you want in vpa.

vpa(pi,12)

ans = 

3.14159265359

vpa(pi,24)

ans = 

3.14159265358979323846264

[Diego Mercado]

Yes, I know that you can do that, but that's not the issue. No matter what number I use, I am always getting 4 digits after the decimal as if I was typing vpa(pi,4), and I've checked with

digits

 
Digits = 32
 

to confirm that I have the default setting of 32.