# how to get the Values from an expression

#Sum of n-th roots of unity is zero.
n=10;
for i in range(1,n):
v=solve(x^i - 1,x);
sum_roots = 0;
m=i;
for j in range(0,i):
sum_roots += v[j];  # error here .. I want the values, not the expression
print ' sum of n-th roots of ' ;
print m;
print ' is ';
print sum_roots ;


How do i get the values from the list of expressions returned by solve? I have another Question-: How can I see all the member functions of any type,say expression..I have tried putting ? sfter the command, but that does not give all the member functions.

edit retag close merge delete

Sort by » oldest newest most voted

Here is another option. I think you are trying to sum the roots of unity.

n=10
for i in range(1,n):
v=solve(x^i - 1,x)
roots=map(lambda q: q.rhs(),v)
print roots
print sum

more

Thank YOU so much!! Could you please tell me where to look for such member functions.. I tried so much to get the rhs of the expression but did not know where to look ! Thanks man!!

( 2014-02-09 10:23:47 +0200 )edit

Glad to help! You can get the member functions by typing the element name, for example myvar, and then a period and hitting tab. So, it would be: myvar.<tab> This will pop up a list of the associated functions. You can then use a question mark to ask for help on that function.

( 2014-02-09 15:09:46 +0200 )edit

It's not clear to me what you want to do. Looking at the first lines of your code: your for-loop ends up with the solutions of x^9 - 1 == 0 ; all other cases are lost. (ok, that's wrong, I can see it now after your code was properly formatted)

n=10
for i in range(1,n):
v=solve(x^i - 1,x)
print v
print solve(x^9 - 1,x)


As far as solve returns a list of equations you can run through the list applying the method rhs() (right hand side)

For example:

sols = solve(x^9 - 1,x)
for sol in sols:
print sol.rhs()


Or (if you are not interested in complex numbers ;-) )

sols = solve(x^9 - 1,x)
for sol in sols:
if sol.rhs() in RR:
print sol.rhs()

more