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Jul
29
comment Is this (funny) combinatorial optimization problem NP-hard ? (cutting numbers and placing them in urns)
At first blush, seems reducible to integer programming, which would make it $\in \mathcal{NP}$. Whether you could reduce something else to it, is a different story. Perhaps by setting $C=1$ you can get a special case like the Knapsack or something like that?
Jul
29
comment Slow convergence simulating log-normal sample from the normal
You are right, it is all about a long tail. I tried it with billion entries, and mean looks ok to 5 digits, but st. dev. is still all over the place. Increasing the mean to 0.05 already matched the st.dev. to 3 digits at 1 mln trials, and doing down to 0.005 with 1 billion trials is not enough... I wonder what the relationship there would be...
Jul
29
comment Distribution of test scores calculate cutoff given mean and standard deviation
Hi, welcome to Math.SE! We don't like to do your homework for you :), so could you please update your question with your thoughts/attempts to do the problem and we will be happy to guide you further.
Jul
29
comment Interest Question
I got 70902.58 for the same calculation
Jul
29
comment Interest Question
Also, what is interest "p.a"?
Jul
29
comment Interest Question
Hi, welcome to Math.SE! We don't like to do your homework for you :), so could you please update your question with your thoughts/attempts to do the problem and we will be happy to guide you further
Jul
29
comment Plotting Distance Constrained Points on a Plane
may be an interesting post on StackOverflow, someone with lots of experience in embedding algorithms may be able to contribute
Jul
29
comment Shortest Path Length as mathematical function/expression
the only thing i can think about is $X^n_{ij}$ is the number of $i \to j$ paths of length exactly $n$
Jul
29
comment Finding the horizontal and vertical tangents of a parametric equation.
@Alex updated solution with another approach for you
Jul
29
comment Finding the horizontal and vertical tangents of a parametric equation.
@Alex horizontal tangents have $y'=0$ so you end up with $x=0$ or $x^2+y^2=1$
Jul
29
comment Express as a single logarithm
Welcome to the site. People here don't like to do your homework for you. Please take some hints in the answer below, attempt the problem and put an update into the question or alert the answerer by a comment...
Jul
29
comment Implicit finite differences: Sufficient conditions for non-negativity
it seems $a_n, b_n, c_n \ge 0$ should do it, but it's too restrictive for you.
Jul
29
comment Implicit finite differences: Sufficient conditions for non-negativity
@uranix he is going back in time
Jul
28
comment Differentiability of multi-variable functions
@user160492 not exactly. Note that $f(0,y)=0$ but $f(x,0) \neq 0$. Can you compute $\frac{df(x,0)}{dx}$?
Jul
28
comment Mathematics of Magic Squares
Welcome to Math.SE! Hope you stay and contribute to the site :)
Jul
28
comment Sign of eigenvalues of $A$ by $\det(A-\lambda I)=\lambda \det(B+D-\lambda I).$
You likely mean $D$ not $C$ in the first sentence
Jul
28
comment Partial differential equation
you could find it numerically, do you need an analytic solution?
Jul
28
comment Partial differential equation
i edited to the best of my ability to understand, please check this is what you intended to ask
Jul
28
comment defining a sequence of numbers L n≥1, and prove something about it
@Zero you can, but I don't see how this will help
Jul
28
comment defining a sequence of numbers L n≥1, and prove something about it
@Zero note that $\phi$ and $\Phi$ both satisfy $x^2 = x+1$. Can you use this fact to complete the proof?