Evaluation of a function and it's inverse with parameters

asked 2020-04-20 12:13:36 -0500

Cyrille gravatar image

updated 2020-04-20 12:46:16 -0500

The following code works perfectly :

var('W1, W2, Ub, p')
a, x, y = SR.var('a,x,y')
W2=W
U(x)=x^a

    assume(a, 'real')
    assume(a, 'noninteger')   # or alternatively 'integer'
    assume(x, 'real')
    assume(y, 'real')
    assume(x > 0)
    assume(y > 0)
    U(x).substitute(x==y)
    show(U(x))
    V=solve(x == U(y), [y])[0].rhs().function(x)
    show(V)
    VV=((Ub-p*U(W2))/(1-p))^(1/a)
    show(VV)

But now I want to be also able to attribute some values to the parameters and the variable to achieve an evaluation and plot according to the parameter values. I need the function and it's inverse. I have seen the methode lambda x in the documentation but it's end with an error.

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Comments

Please use minimal code to illustrate and explain the issue. Which is the function involved, and why are we not defining it explicitly? Do we need a and W2 for instance? What is W above? If we do not need them, please do not mention them. Do we need indeed the many assumed properties? (Or only the one in a...) If yes, there must be a big magic to have them also in the function V. The line with V = ... is a big adventure, this is not a good style to introduce things in a clear manner. Why not defining V explicitly when...

forget()
var('a,x,y');
assume(a, 'real')
assume(a, 'noninteger')
assume(x > 0)
U(x) = x^a
V = solve(x == U(y), [y])[0].rhs().function(x)

sage: V
x |--> x^(1/a)
sage: V.subs( {a : 2} )
x |--> sqrt(x)
dan_fulea gravatar imagedan_fulea ( 2020-04-21 09:01:57 -0500 )edit