How makes all low values in the symbolic calculation become zero?

Question

How can I make all low values in a SymPy expression zero? For example, my result is:

1.0*a1*cos(q1) - 6.12e-17*(a2*sin(q2) + a3*sin(q2 + q3) + a4*sin(q2 + q3 + q         


        

Answer 1

Probably there are much more efficient ways(I am not familiar with that library) but I tried to do with regex. If e- exist in a part of the equation it replaces it to 0(you can remove directly if you want). But to be able to do this, I had to remove to spaces between +- operators inside the parentheses, so I could make a list by splitting from the other +- operators.

import re
result='''1.0*a1*cos(q1) - 6.12e-17*(a2*sin(q2) + a3*sin(q2+q3) 
+ a4*sin(q2+q3+q4))sin(q1) + 1.0(a2*cos(q2) 
+ a3*cos(q2+q3) + a4*cos(q2+q3+q4))*cos(q1)'''
too_small='e-'

mylist=re.split(r"\s+", result)

for i in range(len(mylist)):
    if too_small in mylist[i]:
        mylist[i]='0'

new_result=''.join(mylist)
print(new_result)

And this is the output:

1.0*a1*cos(q1)-0+a3*sin(q2+q3)+a4*sin(q2+q3+q4))sin(q1)+1.0(a2*cos(q2)+a3*cos(q2+q3)+a4*cos(q2+q3+q4))*cos(q1)

As I said, there are probably much better ways than this.