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pythonsympycalculus

Sympy - limit() Error: Result depends on the sign

I'm attempting to solve the following problem:

enter image description here

Applying the following I get the correct answer. 

α, t, x = symbols('α t x')
integrate(α*x*exp(-α*x), (x, 0, oo), conds='none')

To check the solution (1/α) I attempted the following.

limit(integrate(α*x*exp(-α*x), (x, 0, t), conds='none'), t, oo)

But this yields NotImplementedError: Result depends on the sign of -sign(α) as well as a further **NotImplementedError** with no description. The function works for real numbers but not oo. How can I work around this problem?

Solution

  • Adding the argument positive = True to the symbols function mitigates this issue. 

    α, t, x = symbols('α t x', positive = True)

func = integrate(α*x*exp(-α*x), (x, 0, t), conds='none')

(limit(func, t, oo))

    Yielding 1/α