# Search results

1. ### 12VDC/2A power adapter to power two systems?

Hey! So I have a raspberry pi that uses 5V/1.2A and a LCD monitor that uses 12v/0.2A. I would like to power both using a single wall power outlet. I found a power adapter that converts 100-240VAC/50-60Hz/1.2A to 12VDC/2A. I was wondering if it is as easy as cutting off the connector on the...
2. ### MATLAB Solve Riccati (DARE) with MATLAB

Hey all, I was wondering if you can help me define the arguments for the dare() function of matlab. Here is the DARE form I have: \begin{equation} \begin{split} \Phi(p_\infty) &= \Phi_\infty = \Phi_{33}-\Phi_{32}(\Phi_\infty+\Phi_{R})^{-1}\Phi_{23}\\...
3. ### A Derivative of log of normal distribution

Hey all, I've had this point of confusion for a bit and I have thought that with time I may be able to clear it out myself. Nope, hasn't happened. I think I need help. Let us say we have the following \phi_{k+1}=\phi_{k}+v_k where, v_k\overset{iid}{\sim}\mathcal{N}(0,\sigma^2) and...
4. ### A Hessian of f(x)^T*Q*y

Hey all. Let me just get right to it! Assume you have a function f:\mathbb{R}^n\rightarrow\mathbb{R}^m and we know nothing else except the following equation: \triangledown_x\triangledown_x^Tf(x)^TQy=0 where \triangledown_x is the gradient with respect to vector x (outer product of two gradient...
5. ### A Conditional expectation and covariance of function of RVs

Hey all, I have been doing some math lately where I need to find the conditional expectation of a function of random variables. I also at some point need to find a derivative with respect to the variable that has been conditioned. I am not sure of my work and would appreciate it if you guys can...
6. ### I Gradient of ||f(x)||^2

Hey, I have been trying to figure out how to solve \triangledown_x ||f(x)||^2_2. I have used the chain rule (hopefully correctly) to get the following: \triangledown_x ||f(x)||^2_2=2\triangledown_xf(x)^T \frac{f(x)^T}{||f(x)||_2} Is this correct? The reason I doubt my answer is because I know...
7. ### A What is the identity?

Hey all. So I think I've been trying to figure this out longer than I should, that is why I am here now. I was reading an ieee paper and have been pondering a missing proof (the paper deems this proof too easy to show, literally... I must be really stupid or something). It is a simple question...
8. ### When is the gram matrix positive definite?

Hey all. I know that A^TA is positive semidefinite. Is it possible to achieve a positive definite matrix from such a matrix multiplication (taking into account that A is NOT necessarily a square matrix)?
9. ### Constraint on M to keep M^T * A * M positive semidefinite?

Hey all! Let me get right to it! It is given that $$A \succeq 0$$ I need the following to hold for M: $$M^TAM\succeq 0$$ What are the constraints or conditions on M for M^TAM\succeq 0 to hold? Anything would help at this point... I am open to discussion. Note: It may be worth mentioning that...
10. ### Changing to SDP (optimization)

Hey all. Let me get right to it! I have the following objective function: \mathbf{minimize} \ \ trace((G^TG)^{-1}) I am trying to minimize it with CVX. I used schur complement to do the following: \begin{equation*} \begin{aligned} & \underset{G}{\text{minimize}} & &...
11. ### Linear algebra and choosing training vector

Hey all. So I have been reading this article and have a question I would like to ask. I will be referring to this article extensively so it would be kind of you to open it: http://www.ee.ucr.edu/~yhua/MILCOM_2013_Reprint.pdf I believe reading the article is not required to answer my questions...
12. ### Independent elements of matrices?

Hey all. I am currently reading an article and there is a paragraph that I am having a hard time understand. This is what the paragraph says: "Since Ar = Arτ and Ai = -Aiτ, we know that only the lower triangular (including the diagonal) elements of Ar are independent and only the strictly lower...
13. ### How to find transfer function of real world system?

Hey all! I am trying to figure out how one goes about to try and find the transfer function (impulse response) of a real life system. Assuming the system is LTI. This "system" I speak of is a channel that is comprised of components such as linear amps, a mixer (can we even assume a mixer is...
14. ### Engineering Differential Mode Gain and 1/2 circuit

Hey all! I have been trying this problem for a while and can't seem to get the same answer as the solution. If someone can tell me where I am going wrong, that would be much appreciated. I am very close to the solution, but I am missing a term in the denominator. Everything is shown below! Thank...
15. ### Input Resistance of Common Gate question...

Hey all. I have been trying to calculate the input resistance of a common gate amplifier, but seem to have problems doing so. I know I have to set a test voltage (or test current) at the input, and I've been told, to ground the output. So using the Hybrid pi model for a mosfet, I did the...
16. ### Entropy question for 2 input 1 output system

Hey all. I have a question regarding the solution to a question, both shown below (only part of the solution is shown). Specifically the line that states: H(Y|X) = H(Z|X). Why does this equality hold? Expanding and using the definition of entropy, I can see that for the above equality to hold...
17. ### Double sum of same variable simplification help

Hello all, I have been meditating on this for a while, but can't seem to understand how this simplification came to be. Any help will be greatly appreciated. So, here is what we start with: ##\mathop{\sum_{k=0}^m\sum_{l=0}^n}_{m{\geq}n} x(k,l)## We also know that: l (lower case L) = n-m+k and...
18. ### Op-Amp convex optimization question

Hey all. I have a question regarding an equation in a document I am reading about convex optimization of OP-AMPs. The document is attached, the equation is of section 3.4 and the equation number is (9). Can you please explain how it came to be? I understand that i3 = i4 = i5/2 but I don't...
19. ### C/++/# C++ and pthread simple program help

Hey all. I am currently trying to brush up on my multithreading "skills" (I dare say) that I learned in my undergrad class. I have the following code that I am trying to run: #include <pthread.h> #include <iostream> using namespace std; void* func1(void*); int main(int argc, char** argv){...
20. ### Is this a convex set?

Homework Statement Show if the set is convex or not! S2 = Homework Equations I know that to show a set is convex you can either use the definition or show that the set can be obtained from known convex sets under operations that preserve convexity. Convex definition: x1*Theta + (1 -...
21. ### Matrix derivative of quadratic form?

Homework Statement Find the derivative of f(X). f(X) = transpose(a) * X * b where: X is nxn a and b are n x 1 ai is the i'th element of a Xnm is the element in row n and column m let transpose(a) = aT let transpose(b) = bT Homework Equations I tried using the product rule...
22. ### Operator change of basis

Homework Statement Homework Equations \check{T} = BTB^{-1} (eq1) The Attempt at a Solution Ok, so I have a couple of questions here if I may ask... First, I want to be sure I understand the wording of (a) and (b) correctly. Is the following true?: (a) Write the matrix T...
23. ### Dual gate mixer help

Hello all. So i have been trying to simulate a ndg transistor mixer in LTSpice. Here is what I have so far, but I am missing something and I can't figure what it is... Here is the schematic along with the waveforms. For some reason the output will not go over 0.3V (do I have to bias it?)...
24. ### IF amps for a superhet AM receiver

Hey all. So I am now trying to work on IF amps for a superhet AM receiver (medium wave) and found the following figure in the ARRL handbook: I have a couple of questions regarding these schematics. First and most importantly, do these work for IF signals (of 455KHz with BW of 18KHz)...
25. ### DBM: Ring Diode Topology

Hi all. I started a thread a while back about RF mixer design. I didn't know what to do or what design to choose. You guys laid some options for me and after some research and time I have finally decided that I will go for a double balanced, ring diode topology. Here is a schematic from google...
26. ### Cascode Amp questions

Hello all. I have been looking into RF amps. I have come across the following cascode amp (from ARRL handbook 2014, p 12.10, FIG. 12.11. Thanks to Baluncore for the great reference). Here is a simplified version made with Qucs: My questions are regarding the capacitors, C1 and C2. Why are...
27. ### Controls VS. Communications (EE)

Hey all. I will get straight to the point. I am about to get into graduate school and I have the option to choose between Controls & Robotics OR Communication & Signal Processing. I am kind of not sure what to pursue, the reason is because I feel if I choose one I will unfortunately lose the...
28. ### RF Mixer circuit help

Hello all. So I have been trying to build a mixer lately, I have done my research on google but I am still kind of lost. I know now many mixers exist; single diode, multiple diodes, single balanced, double balanced, unbalanced and so on. I don't want to build a circuit blindly, so I am trying to...
29. ### High power switching circuit problem.

Hello all. I am trying to use a mosfet as a high power switch. I have an arduino nano pin controlling the gate of the fet. I am using an NTE2374 mosfet. I am using a typical circuit: I also have the gate connected to the source (ground) so that when the gate is not HIGH, it isn't floating...
30. ### Power spectral density math

Homework Statement For now I am trying to find the power spectral density only. The Attempt at a Solution From the given graph, I got g(t) = -1 + 2rect(t/2), with a perdiod of 4s PSD = Sg(f) = lim(T \rightarrow\infty ) \frac{1}{2T} || G(f) || ^{2} My fourier transform of g(t), G(f), I...