using the value of a symbolic expression

[jean-pat]

Hello,
After having solved an equation, I'd like to use the result for another calculation (calculating y) or a ploting.
How to convert sol into a numerical value?

thank you

jeanpat

sol=solve(2*x+1==7,x)
print sol
print sol[0], type(sol), type(sol[0])
#y=2*sol+7
#print y

#plot(sol,0)

[Vincent Knight]

You can do two things jeanpat:

1:

sol=solve(2*x+1==7,x, solution_dict=True)

print sol  # sol is a list of dictionaries (key: variables, value: solution value)

print sol[0][x]

2:

sol=solve(2*x+1==7,x)

print sol  # sol is a list of equations

print sol[0].rhs()  # takes the first (and only on this occasion) equation of your solution and take the right hand side (rhs) of it.

Vince

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Dr Vincent Knight
Cardiff School of Mathematics
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+Vincent Knight
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[jean-pat]

thank you for your help,

Doing print sol[0].rhs() failed on http://sagecell.sagemath.org with the message:

AttributeError: 'Sequence_generic' object has no attribute 'roots'

But the first method worked