Round polynomial coeff symbolic

Question

amin ya 2019-7-8

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/470723-round-polynomial-coeff-symbolic

回答： amin ya 2019-7-8

As built in Matlab lacks this, I have written a code to find coeffitients that are very small:

function symRound=coeffRounder(symExp)
% search all elements of a matrix
for i=1:size(symRound,1)
    for j=1:size(symRound,2)
        
        [C,T]=coeffs(symRound(i,j));
        isSmall=logical(abs(c)<1e-16);
        
        C(isSmall)=0;
        symRound(i,j)=dot(C,T);
        
    end
end
symRound=symExp;
end

Is there any way to avoid this and solve the problem without this function?

This is caused because of

syms x
cos(-pi/2)*x

I also used the 2nd and 3rd syntax from here:

https://www.mathworks.com/matlabcentral/answers/437316-weird-behavior-regarding-pi-in-symbolic-expressions

Pi = sym(pi, 'f')     %if you want it treated as 884279719003555/281474976710656
Pi = sym(pi, 'd')     %if you want it treated as symbolic 3.1415926535897931159979634685442

Non of them gives 0 for