# Finding the Unique Solution of a Polar System with Variable Radius?

• MHB
• Jiggerjaw
In summary, the conversation discusses finding the starting phi0 given (phi, r) and an equation that determines phi based on the initial phi0 and a variable radius. Laplace transforms can be used to solve this type of differential equation if the boundary conditions are defined, which can be done by finding the initial phi0. The conversation also mentions the use of Laplace transforms in polar coordinates and the need to treat r<0 and r>=0 as separate systems.
Jiggerjaw
Hello! Brand new to the forums, hopefully someone here can help me out.

Paths start out at the edge of a circle and "flow" along a polar equation that determines phi based off the initial phi (phi0) and a variable radius (ie. as your radius grows, your phi is changing). Hopefully this image can clear up the questionable wording:

For example, for the point labelled "-100" . It's located at ~(-170 degrees, 25) but it started at whatever the initial radius is (r0) with a 100 degree "trajectory".

In reality, these aren't actually trajectories. It's just a map (axons in a human eye)... I need to figure out how to find the starting phi0 given (phi, r) and this equation:

(where b and c are equations of phi0 with a different equation if r<0 or r>=0)Is this possible? I know the first step is treat it as two separate systems. One where r<0 and one where r>=0. It seems that Laplace for polar coordinates requires a fixed radius. Maybe I'm reading into it wrong though. Every video I've found on Laplace in polar coordinates is talking about signals and I'm not at all familiar with electrical engineering. I have a fairly good understanding of Linear Systems but this problem is tripping me up. I'm having trouble grasping how to work with it when there are intermediate radii between r and r0 but both r and r0 can be treated as constants since they are known values.

Sorry for the ambiguity, I'm not posting the exact equations as I'd really like to work this out on my own. Just need a push in the right direction (and hopefully not told that it's impossible).

Thanks in advance!It sounds like you are trying to solve a differential equation with boundary conditions. You can use Laplace transforms to solve this type of equation, as long as you can define the boundary conditions for your system. To do this, you need to find the initial phi0 given (phi, r) and then use that to define the boundary conditions of your system. Once you have done this, you will be able to use Laplace transforms to solve the equation.

Hi there! Welcome to the forums. I'm not an expert in polar equations, but I'll try my best to help you out.

To find the starting phi0 given (phi, r) and the equation you provided, you will need to use the inverse function of the equation. In other words, you need to solve for phi0 in terms of phi and r.

Since you mentioned that you need to treat r<0 and r>=0 as two separate systems, I'm assuming that the equation you provided has two different forms for these two cases. So, you will need to solve for phi0 separately for each case.

For the case where r<0, you can use the inverse function of the equation for r<0 to solve for phi0. And for the case where r>=0, you can use the inverse function of the equation for r>=0 to solve for phi0.

Once you have the two values for phi0, you can compare them and choose the correct one based on the given phi and r values.

I hope this helps! Let me know if you need any further clarification. Good luck with your problem!

## 1. What is a polar system with variable radius?

A polar system with variable radius is a mathematical system that uses polar coordinates to represent points in a plane, where the distance from a fixed point (the pole) and the angle from a fixed direction (the polar axis) are used to determine the location of a point. In this system, the radius can vary, meaning that the distance from the pole to the point can change.

## 2. Why is it important to find the unique solution of a polar system with variable radius?

Finding the unique solution of a polar system with variable radius is important because it allows us to accurately determine the coordinates of a point in the plane. This is especially useful in fields such as engineering, physics, and navigation, where precise location information is crucial.

## 3. How do you find the unique solution of a polar system with variable radius?

To find the unique solution of a polar system with variable radius, you must first convert the polar coordinates into rectangular coordinates. This can be done using the conversion formulas r = √(x^2 + y^2) and tanθ = y/x. Once the coordinates are in rectangular form, you can solve for the variables and find the unique solution.

## 4. Are there any special cases when finding the unique solution of a polar system with variable radius?

Yes, there are two special cases to consider when finding the unique solution of a polar system with variable radius. The first is when the radius is equal to zero, which means the point is located at the pole. The second is when the angle is equal to zero or a multiple of π, which means the point is located on the polar axis.

## 5. Can a polar system with variable radius have more than one solution?

No, a polar system with variable radius can only have one unique solution. This is because each point in the plane can only have one set of polar coordinates, and the conversion to rectangular coordinates is a one-to-one function. However, it is possible for different points to have the same polar coordinates, resulting in multiple points with the same unique solution.

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