# Recent content by Soveraign

1. ### Probability Density of a Constrained Chi-Square

Thought I would follow up here and try to more succinctly describe the problem. At its core, I have three random variables that are normally distributed: x_1 \sim N(\mu_1, \sigma_1) \\ x_2 \sim N(\mu_2, \sigma_2) \\ x_3 \sim N(\mu_3, \sigma_3) I also know there is a relationship among...
2. ### Probability Density of a Constrained Chi-Square

Thanks for the reply. I do check assumptions about distributions with high-stat simulations to try and catch mistakes. In the situation I'm describing above, it is the high-stat sims that show I must be doing something wrong... but not horribly so. I have both a bias in my final results as...
3. ### Normal distribution negative values

I run into this issue with my research when modeling particle detector responses with a normal distribution since it will on occasion try to produce a negative energy particle (clearly not realistic). There are options but they produce biases. One is to just cap the low end at zero (or nearly...
4. ### Probability Density of a Constrained Chi-Square

Hello PF! It's been a while. How are things? In my research I'm faced with determining a probability distribution from a function built as follows: Perform three measurements X, Y, Z that have normally distributed errors. Impose a constraint and variable change that allows me to...
5. ### How to move forward with a less than perfect undergrad gpa

Sometimes you can get in (not top tier) with less than 3.0 on probation. Your scores on the Physics GRE would probably be a primary factor. Depending on the school you may even hedge your bet a little and apply for M.S. program, then move on to the Ph.D. after a couple semesters once you've...
6. ### How difficult is it to get a research job in industry?

I suppose that depends. Are you still an undergrad? In grad school? If an undergrad, taking classes certainly wouldn't hurt. Full disclosure: I have degrees in both comp sci and physics so I'm biased. I have found the comp sci background to be extremely useful since I encounter multiple...
7. ### How difficult is it to get a research job in industry?

Yes, yes, and yes. Those three are a good start ;) C++ and Java are very close in structure and syntax, so not a big deal to know both. Python is just, well, awesome. Ok, not in all aspects, but for certain things (fast prototyping of an idea) it is. Plus it's really easy to learn.
8. ### Programs Can a non-physics major pursue graduate physics program?

Your situation sounds very familiar. My first degree was Computer Science. I actually went back to get an undergrad in Physics before going on to grad school. It took four semesters because of the class sequence (I also picked up a math degree while I was at it). In my school, IF one...
9. ### Using Correlation to Predict Values

If I understand the definition correctly, then I think so. Y, A, B, C are normally distributed about a mean, but not necessarily independent (i.e. covariance != 0). A thought I had was to perform principle component analysis on A, B, C so I then would have some new (independent) eigenvectors...
10. ### Using Correlation to Predict Values

You are correct, I am looking to calculate the expected value of Y given A, B, C and known correlations YA, YB, YC, AB, AC, BC (and necessary variances, etc...)
11. ### Using Correlation to Predict Values

I've searched the forums but am unable to find an answer to this: Given two variables with a correlation, you can predict one from the other using the familiar E(Y|X) = EY + r * s_y * (X - EX) / s_x What I want to know is how to predict values from multiple variables, especially when these...
12. ### 3D Programming

I very briefly did some exploration working directly with OpenGL, but it seemed like a ton of work to handle things at that level. So then I learned 3D in Java using java3d. I found a tutorial and very diligently followed it step by step. A few days in, I was able to do some cool stuff from...
13. ### Enumerating Combinations

I am facing an issue in my research where I need to enumerate all combinations of an underlying set. BUT the set has some special features. Here is an example: Given a set {A,B,C,D,E, F} where each item in the set consists of two values. Something like: A = (1,2) B = (3,4) C = (5,6)...
14. ### Phenomenological aspects of ultra-high-energy collisions

It's true, lepton-lepton collisions are much nicer to deal with. Plus *all* center of mass beam energy is available to make a particle (which is generally not the case for hadrons). You need to have much more energy in your hadron beam than the energy of physics you are actually exploring...
15. ### Quick help with NUCM of a disc

Centripetal acceleration is acceleration directed towards the center of circular motion. So this is usually a_c=-\omega^2 r or a_c=-\frac{v^2}{r}. In either case you need to know how fast the disc is rotating (and its radius). So how would you determine how fast the disc is...