# How to tell vpa command to consider digits after decimal point' only?

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Mohammad Shojaei Arani on 28 Dec 2021
Answered: Walter Roberson on 28 Dec 2021
Hello friends,
I have a simple question, I think! I have a symbolic expression S with numeric coefficients. I need to round the coefficients
up to some digits 'AFTER DECIMAL POINT' only (note that I do not know, beforehand, how many digits my numbers have, so, I want to keep all digits before decimal point and a few after that). So, if I use vpa(S,4) then it only considers 4 digits in total and does not respect my what I want. Let me use a simple example as bellow:
syms x y
f=34344.4545*x+45.6566*y;
now, vpa(S,4) gives me
34340.0*x + 45.66*y
and this is not what I want since the first coefifcient is badly rounded. Of course, in this exmple I could use vpa(S,8) to get 34344.454*x + 45.6566*y but please note that "I do not know, beforehand, how many digits my coefficients have in general".
Any idea?
Babak

Walter Roberson on 28 Dec 2021
syms x y
f = 34344.4545*x+45.6566*y;
newF = mapSymType(f, 'constant', @(v) round(v,4))
newF = 