How do I assign variables from the solution of an equation?

assign
solve

I was pleased to see how easily Sage solves systems of equations. For example, evaluating:

var('A,B')
f(x) = A*x + B
solve([f(3) == 5, f(7) == -3], A, B)

yields:

[[A == -2, B == 11]]

With a little text editing, I can use that solution to define f, which I can then plot or use to solve other equations:

A = -2; B = 11
f(x) = A*x + B
...

Is there a way to make the assignments of A and B (or more directly, f ) from the solution of the linear equations, without the copy+paste+edit step?

add a comment

2 Answers

Sort by » oldest newest most voted

answered 12 years ago

William H. Hooper
1 ●1 ●1 ●2

Thanks to kcrisman (http://ask.sagemath.org/question/347) I found a method using loops:

var('A,B')
f(x) = A*x + B
sol = solve([f(3) == 5, f(7) == -3], A, B)
for s in sol[0]:
    f = f.subs(s)
...

Now I can plot f, or use it to solve other equations. That's still a little cumbersome, when I have multiple equations to solve and substitutions to apply. If you have a loopless method, please post.

link

add a comment

answered 12 years ago

ndomes

2429 ●1 ●22 ●55

I recommend the option solution_dict=True:

solve returns the solutions as list of python dictionaries and this makes substitution very easy.

var('A,B')
f(x) = A*x + B
sol = solve([f(3) == 5, f(7) == -3], A, B,solution_dict=True)
f.subs(sol[0])

link

add a comment

Your Answer

Please start posting anonymously - your entry will be published after you log in or create a new account.

Add Answer

How do I assign variables from the solution of an equation?

2 Answers

Your Answer

Question Tools

Stats

Related questions

How do I assign variables from the solution of an equation? savecancel

2 Answers

Your Answer

Question Tools

Stats

Related questions

How do I assign variables from the solution of an equation?