how can I set the decimal digits of all coefficients at one time when outputting a polynomial f?

In Windows 10, MATLAB R2018a, I try to use fprintf to output a polynomial f, for example, 5.327416*x^2+3.660092*x+1.5799301. How can I set the decimal digits(e.g. 3) of all coefficients at one time instead of setting them one by one? That is, I want the result to be "5.327*x^2+3.660*x+1.580". Anyone can help me? Thanks!

Answer 1

[Walter Roberson]

 P = [5.327416, -3.660092, 1.5799301]

P = 1×3

5.3274 -3.6601 1.5799

 
 %method 1
 vpa(poly2sym(P, sym('x')),4)

ans = 

 %method 2
 poly2sym(round(sym(P),3))

ans = 

 %method 3
 fmt = [repmat('%.3f*x^%d + ', 1, length(P)-1), '%.3f\n'];
 temp = reshape([P; length(P)-1:-1:0], 1, []);
 fprintf(fmt, temp(1:end-1));

5.327*x^2 + -3.660*x^1 + 1.580

If you want the + -3.660 to instead show up as - 3.660 then it takes more work.

[marvellous]

Thanks! Your answer really helps.

[Dyuman Joshi]

You can use disp on the symbolic expression or convert it to char and use fprintf as well -

P = [5.327416, -3.660092, 1.5799301]

P = 1×3

5.3274 -3.6601 1.5799

y = vpa(poly2sym(P, sym('x')),4);

disp(y)

z = char(y);
fprintf('%s', z)

5.327*x^2 - 3.66*x + 1.58

[marvellous]

Bravo! Many thanks!

Answer 2

[Sam Chak]

a = 5.327416;
b = 3.660092;
c = 1.5799301;

fprintf('f(x) = %.3f*x^2 + %.3f*x + %.3f', a, b, c)

f(x) = 5.327*x^2 + 3.660*x + 1.580

[marvellous]

Thank you for your help, but this is not what I want. Since I may not know the degree of f, I can not write out the 'x' items in advance. Thus, I do not intend to set the decimal digit for each coefficient separately. I prefer to write like ' fprintf (' ? ' , f) ', but I can not figure out what to fill in at the question mark to make it work? Can you help me?