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Computational Science : Recent Questions and Answers (Page 20)

Find answers to your questions about Computational Science or help others by answering their Computational Science questions.

Why is the problem infeasible?

Given $mathbf V_t=mathbf v_tmathbf v_t^H$ where $mathbf v_t=left(e^{jtheta_{1}},e^{jtheta_{2}}right)^H$:begin{equation*}begin{array}{ll}underset{mathbf V}{operatorname{minimize}} & 1text { subject to } & operatorname{diag}(mathbf V)=1&|mathbf V|_*-operatorname{trace}left[boldsymbollambdaboldsymbollambda^Hleft(mathbf V-mathbf V_tright)right]-|mathbf V_t|_2leq...

Asked on 05/30/2021 by fengbiqian

0 answer

Is there any function to calculate condition number of sparse matrix in Eigen libraray?

The function JacobiSVD and BDCSVD can calcuate condtion number of a dense matrix via singular values.However I need to know condition number of a sparese matrix due to slow...

Asked on 05/28/2021

0 answer

Efficient change of basis real positive definite symmetric matrix

I need to optimize a code where the most performance critical part is doing a 'change of basis', in other words it is an unitary similarity transformation on a big...

Asked on 05/28/2021 by Vittore Scolari

1 answer

When is a dynamical system periodic?

Say a system of ODEs describing a dynamical system, with solutions/state-space vectors ($x$, $y$, $theta$). If values of $y$ and $theta$ repeat but values of...

Asked on 05/27/2021

1 answer

Computing size of N-Dimensional Polynomial Basis and Efficient Representation of Basis

A problem I have had on my mind recently has been a compact way to compute the size of an $N$-Dimensional Polynomial basis of some order $p$, where a linear...

Asked on 05/26/2021 by spektr

2 answer

An efficient algorithm to find Nearest Neighbours

So imagine I have a $m$ vectors each of dimension $d$. Lets call them, $vec x_{i}$, with $i = 1, 2, 3, 4, 5, dots, m$....

Asked on 05/24/2021

1 answer

Choice of iterative solver for a sparse asymmetric matrix with symmetric structure

I have a sparse $nxn$ matrix A with pretty interesting structure. It has a block structure with symmetric structure but asymmetric blocks. Expressed mathematically $A_{jk} = A_{kj}$ but...

Asked on 05/21/2021

0 answer

Energy cannot decent during optimization despite non-zero gradient

Assume we have an (at least) 2nd-order differentiable energy $f(x), xin R^n.$ And $n$ is very big. Mathematically, I think it is impossible to find a point ...

Asked on 05/21/2021 by user3677630

0 answer

Imposing total pressure over surface in FEM

I am trying to solve Stokes problem using Finite element method. My question is how to impose that total pressure over the surface is zero to remove the constant pressure...

Asked on 05/20/2021 by Eda Suresh Reddy

2 answer

Method of Lines: How to simplify Jacobian with periodic BCs?

Consider the advection equation$$frac{partial u}{partial t}+c(x)frac{partial u}{partial x}=0.$$With periodic boundary condtitions in $x$ with period $L$, i.e. $u(x,t)=u(x+L,t)$ and initial condition $u(x,0)=f(x)$.We...

Asked on 05/18/2021

1 answer

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