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 Feb 3 comment How do you show a set is dense? For example, is the set of all ration numbers $p/q$ with $q ≤ 10$ a dense set? It is the minimal distance between two numbers of your set. What would you expect for a dense set? Feb 3 comment How do you show a set is dense? For example, is the set of all ration numbers $p/q$ with $q ≤ 10$ a dense set? If you restrict $q$ to be smaller than $10$, how close could you for example approximate $0.15$ in the best case? Feb 2 comment Accelerating linear solve in MATLAB for a specific type of matrices The system is indeed not sparse, just very small. MATLAB will be left behind later on, this is just for testing purpose, however a faster code would also allow better testing. Thanks for the reference, I will take a look at it! Feb 1 asked Accelerating linear solve in MATLAB for a specific type of matrices Jan 1 revised Largange polynomial second order derivative added 14 characters in body Dec 16 answered Largange polynomial second order derivative Dec 8 awarded Popular Question Dec 6 comment Quadratic optimization: Why does the formula have “$\frac{1}{2}”$ in front? Usually the $\frac12$ is due to the fact that it vanishes when differentiating w.r.t $x$. Nov 16 comment existence directional derivatives Do you know the definition of the directional derivative? Nov 12 awarded Yearling Nov 12 comment Which functions are in $C_0^\infty$, except for the Bump function Thanks for all the comments, I feel stupid for not realizing, that I could just combine $\phi$ with another function. If any of you would take the time to write your comment as an answer I will gladly accept it. Thanks! Nov 11 asked Which functions are in $C_0^\infty$, except for the Bump function Oct 14 revised Equation - what first? deleted 34 characters in body Sep 20 comment How can I find the convolution of these two functions? @B.Lee , I didn't go through the calculation, but I would split the integral at $t$, i.e. $\int_{-\infty}^\infty = \int_{-\infty}^t + \int_t^\infty$. Sep 20 comment How can I find the convolution of these two functions? I would consider the cases $t<0$, $t=0$ and $t>0$. Then you can split the integral with $t$ dependency. Aug 29 comment How do i evaluate $\bigtriangleup^{10}(1-ax)(1-bx^{2})(1-cx^{3})(1-dx^{4})$ I'm not exactly sure, what you are planning to do, but if the differentiation is of order 10, you might want to check the maximum order of your polynomial. Aug 6 revised Approximation of a negative exponential model? edited body Aug 6 answered Approximation of a negative exponential model? Aug 3 comment Consider the function f(x)=sin(x) in the interval x=[π/4,7π/4]. The number and location(s) of the local minima of this function are? The reason, why $\pi/4$ might sound confusing, is because it is no global minimum, but a local minimum at the left boundary. Aug 3 comment Consider the function f(x)=sin(x) in the interval x=[π/4,7π/4]. The number and location(s) of the local minima of this function are? Thanks for adding the local minima at $\pi/4$. +1