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Jul
14
revised Findfit doesn't give the good fit; Changing the starting values will not change the results
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Jul
14
answered Findfit doesn't give the good fit; Changing the starting values will not change the results
Jul
14
answered Reduction of repetitive calculations in Table
Jul
14
comment Simple differential equation to solve
note you have the same issue with D[x[Te, w], Plocal]. x[Te,w] has no apparent dependency on Plocal so this is zero, hence your equation as written is just ` 1 + 0 == 0 ` which just evaluates to False
Jul
14
comment Simple differential equation to solve
Te is an undefined symbol, so that D[Te, Plocal] immediately evaluates to zero (ie before Solve starts to work on it). You need to tell mathematica Te depends on Plocal, ie. use D[Te[Plocal], Plocal], or likely better dont use D function at all and use a symbol such as dTedPlocal both in the equation and in Solve
Jul
14
comment Distance between data and curve
just fyi a high order polynomial is usually a terrible way to approximate data. You will tend to hit the points well and deviate wildly in between.
Jul
12
comment How to make Mathematica save all open files, or automatically ask to save each file when closing
does this change the modification time on every notebook you open even if unchanged?
Jul
12
revised NIntegrate Trapezoid rule with even subdivision producing poor results
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Jul
12
revised NIntegrate Trapezoid rule with even subdivision producing poor results
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Jul
12
comment NIntegrate Trapezoid rule with even subdivision producing poor results
really nice piece of work, but it doesn't relate to the issue at all since the BUG doesn't appear with maxrecursion->0. If you do points->2 recursion->1 you get a completely different result than points-3 recursion->0 based on the exact same sample points.
Jul
11
comment Nonlinear FEM and FindRoot
In the finite element method the numerical integration over the element is typically done using very minimal sampling (i.e. one or two quadrature points). You should not be using NIntegrate , rather work out by hand the 1- or 2- point gauss integration formula and use that.
Jul
11
answered Problem with infinite sum
Jul
11
comment Energy Equation: Boundary and initial condition
your first and third b.c.s are (ideally) inconsistent since one implies dt/dr=0 on x=0 while 3 prescribes d/dr for all x. If you are satisfied with the solution you can ignore the warning. One way to actually fix it is to make the r.h.s of condition 3 a function of x that goes to zero at x=0.
Jul
11
revised Energy Equation: Boundary and initial condition
added 21 characters in body
Jul
11
revised NIntegrate Trapezoid rule with even subdivision producing poor results
added 53 characters in body
Jul
11
answered NIntegrate Trapezoid rule with even subdivision producing poor results
Jul
11
comment NIntegrate Trapezoid rule with even subdivision producing poor results
The issue seems to be only with Points->2 but persists for any MaxRecursion .. (except 0)
Jul
11
comment NIntegrate Trapezoid rule with even subdivision producing poor results
i concur this is a bug with the weights you have surmised. Seems fairly innocuous though, Points-3,MaxRecursion->0 gives the result you want.
Jul
11
comment Plot the results of integrating a complicated Dirac-delta function
@MichaelE2 the integral blows up at the repeated root because the first derivative is zero.
Jul
10
comment Random numbers that sum up to specific value
It will not produce repeated elements to give you zeros from differences. Try it f[9,3] never produces {0,0,9},{1,0,8},..