DE: Lower Bound for radius of convergence

In summary, the conversation discusses a differential equation with three variables, P, Q, and R, and four complex numbers at which P is equal to 0. It is determined that the solutions to the equation can be considered analytic as long as P is not equal to 0, and the distance from 0 to the four complex numbers is 2. This information can be used to determine the radius of convergence for a power series solution centered at 0.
  • #1
BobMarly
19
0
Prb:(x^4+4*x^2+16)y"+4(x-1)y'+6xy=0
P=(x^4+4*x^2+16) Q=4(x-1) R=6x
P=0 for - 1 - 3^(1/2)*i
1 - 3^(1/2)*i
- 1 + 3^(1/2)*i
1 + 3^(1/2)*i
Q=0 for 1
R=0 for 0
Do we ignore Q & R, plotting P, then find shortest distance which would equal 2?
 
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  • #2
Basically, yes. If P were never 0, all solutions to the differential equation would be analytic. Because P is 0 at those four complex numbers, we can take the solution to be 0 away from them. The distance from 0 to those four points is 2 so the radius of convergence of a power series for the solution, centered at 0 wil have radius of convergence 2.
 

1. What is the "lower bound for radius of convergence" in DE?

The lower bound for radius of convergence in DE refers to the minimum value of the radius of convergence for a given differential equation. It is the smallest positive number that determines the interval of convergence for a power series solution of the differential equation.

2. How is the lower bound for radius of convergence determined?

The lower bound for radius of convergence is determined by analyzing the coefficients of the differential equation and using various techniques such as the Cauchy-Hadamard theorem or the Ratio Test. These methods help to find the smallest positive number that guarantees the convergence of the power series solution.

3. Why is the concept of "lower bound for radius of convergence" important in DE?

The lower bound for radius of convergence is important in DE as it helps to determine the range of values for which the power series solution of a differential equation is valid. It also provides information about the convergence or divergence of the solution, which is crucial in solving real-world problems.

4. Can the lower bound for radius of convergence be negative?

No, the lower bound for radius of convergence cannot be negative. It is always a positive number as it represents the smallest interval for which the power series solution of a differential equation converges. A negative lower bound would imply that the solution is valid for negative values, which is not possible.

5. How does the lower bound for radius of convergence relate to the order of the differential equation?

The lower bound for radius of convergence is directly related to the order of the differential equation. In general, the higher the order of the differential equation, the smaller the lower bound for radius of convergence. This means that higher-order differential equations may have a smaller range of values for which their power series solution is valid.

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