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 2h revised No analogue for Maple's dchange? grammar mistakes fixed 5h revised No analogue for Maple's dchange? add examples for expected behavior. 6h revised No analogue for Maple's dchange? added 4 characters in body 6h comment No analogue for Maple's dchange? @m0nhawk Well, as I mentioned above, that's just one of the related questions that are not general enough. 6h asked No analogue for Maple's dchange? 9h comment Integro differential eq boundary difficulties I suggest you to add the $LaTeX$ or screenshot of your original PDE to your question. BTW, a simple mistake is exp should be Exp. 9h comment NDSolve to solve a PDF "Numerically, using the method of lines (the default in this case), condition 1 is not integrated." Yeah, actually this has been (vaguely) mentioned in the possible issue of DiracDelta: Numerical routines will typically miss the contributions from measures at single points. 11h comment Solving coupled differential equations with an eigenvalue What approach do you want to take for finding Ei? b[Ei] actually returns 2 InterpolatingFunction while you only have 1 unknown! If you replace the {ϕ, A} inside ParametricNDSolve with ϕ or A, you'll get a solution, whether the solution is correct or not is another story. BTW, you may want to try this package: library.wolfram.com/infocenter/Demos/4482 12h comment Nest-Recursion leads to overflow - Numerical calculation of Lyapunov exponents It's just an issue of error accumulation. Use a higher precision e.g. 32 will help. To understand why the overflow happened when you set the precision to 16, you can use NestList instead of Nest and remove ;{First[#], Rest[#]} &@Partition[yt, n] from the code and check the result, you'll see the Precision become lower and lower through the numeric calculation. BTW, you don't need Outer for JacobianMatrix, JacobianMatrix[funs_List, vars_List] := D[funs, {vars}] is enough. 2d reviewed Approve Is Sow/Reap compatible with Composition? 2d revised Converting a sum into $\Sigma$ notation improve the format a little 2d revised Converting a sum into $\Sigma$ notation added 385 characters in body 2d answered Converting a sum into $\Sigma$ notation Apr15 comment 3D scatter plot with labels Show[Graphics3D[{Blue, PointSize[0.02], Point[data]}], Graphics3D[ Text[#[[1, 1]], 1.04*#[[2]]] & /@ Transpose@{labels, data}], Axes -> True, BoxRatios -> 1] Apr14 comment Trying to model Heat flow trough different materials with NDsolve BTW, let alone the vagueness of this question, how to Implement heat flux continuity condition is indeed a interesting question, I do find a solution for this, but not that general and I'm not satisfied. I'm hesitating whether I should post it as an answer or start a new question, which will of course state the problem in a clearer way. Apr14 comment Trying to model Heat flow trough different materials with NDsolve Just a sidenote, I believe that OP and @Laurent and this OP did want to add a flux continuity condition, they just didn't understand what a flux continuity condition is very well. Flux continuity condition depends on heat conductivity coefficient (usually notated with $\lambda$) rather than thermal diffusivity (usually notated with $\alpha$, for OP's question, (1 + 4 UnitStep[5 - x])/5. plays the role of thermal diffusivity exactly. ) Apr13 comment Assumptions with patterns @Fabio Well, the above code has been tested in v9.0.1, vista 32bit. Have you tried it with a fresh kernel? Apr13 comment Simplify equations with pattern assumptions It's a pity that psimp doesn't support Subscript or I could mark this question as a duplicate. Still +1. Apr13 comment Assumptions with patterns Which version are you using? In v9.0.1, both of the assumptions failed. And in v8.0.4, the result is on the contrary! Apr13 revised Assumptions with patterns edited title