# User Portlet

Ralph Trenkler
Discussions
I have a question: How does Mathematica compute a derivative numerically by Euler sums in the function "ND", which is found in the numerical calculus package? Which formula is used? Thank you very much!
&[Wolfram Notebook][1] [1]: https://www.wolframcloud.com/obj/2df66d82-177e-4cde-ac06-11457af50577
The important functions in my program are "matrixHN" and "matrixSN". I use the numerical integration method "NewtonCotesRule", because it gives the best results. Is there a better integration method?
I have written a program for the principal axis transformation of quadrics in matrix form with homogeneous coordinates. The Solve command goes into an infinite loop in the third function call of "principalAxisMat" with matrix "A3". It fails to solve...
I wrote a program which finds all finite fields with n elements. For n=2,3,4 this program works very well. It finds only one finite field for n=2,3 and 4. But for n=5 it finds no field. Does my program have a bug? The function "allFields[n]" in this...
Is there any Mathematica command with which I can combine a sum of logarithms into a logarithm of a product? Log[a]+Log[b] -> Log[a*b], Log[a]-Log[b] -> Log[a/b], etc.
How can I change the time limit for a Mathematica Online computation only for one expression? How can I view the current time limit?
I tried to solve the Boltzmann equation in 2 spatial dimensions with NDSolve and the method of lines. In the first call of NDSolve in the attached Mathematica notebook the computation time jumps from 3 minutes for MinPoints -> 19 to more than 5 hours...
I want to transform the expression x*y*Inactive[Sum][1/n^2,{n,1,Infinity}] to the expression Inactive[Sum][x*y/n^2,{n,1,Infinity}] with the symbolic function Distribute : ...
Hello, I installed Mathematica 10 on openSUSE 13.1. With some notebooks the following error occurs: When I try to save the notebook as a PDF file or print it on the printer, then the application crashes with "segmentation violation" and prints out...