6.22.1 Top new questions this week

6.22.1.1 Solving the Lotka-McKendrick model with NDSolve

https://mathematica.stackexchange.com/landing/r/digest?cta=question&id=230366

The Lotka-McKendrick model is a demographic model that represents the way a population changes over time due to fertility and mortality. For an age-specific population density $ u(a, t) $, and a total ... 
[differential-equations] [integral-equations] [ecology]
 

asked by Pillsy https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=531 12 votes

answered by Chris K https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=6358 9 votes

6.22.1.2 Nonlinear dispersal equation modeling insect aggregation

https://mathematica.stackexchange.com/landing/r/digest?cta=question&id=230429

I'm a newbie with Mathematica, I know it's a basic answer, but I can't solve the problem on my own. 
I have the following equation reflecting insect aggregation at low population densities (taken from ... 
[differential-equations] [numerics] [finite-element-method] [ecology]
 

asked by Vefhug https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=74729 10 votes

answered by xzczd https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=1871 17 votes

6.22.1.3 Making a faster alternative for  PatternSequence[1, PatternSequence[2, 3 ..] ..] ..

https://mathematica.stackexchange.com/landing/r/digest?cta=question&id=230622

I need to improve a pattern or switch an approach. 
It is best described by an example 
For a hierarchy/order given by a list e.g.: 
 order = {1, 2, 3} 
 
and a list: 
<... 
[performance-tuning] [pattern-matching]
 

asked by Kuba https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=5478 9 votes

answered by Leonid Shifrin https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=81 9 votes

6.22.1.4 How can I get material property data past what's provided via ElementData[], ChemicalData[], etc.?

https://mathematica.stackexchange.com/landing/r/digest?cta=question&id=230484

Background 
Let's say I want information (e.g. bulk modulus or space group) on an element or chemical compound that isn't available via e.g.  ElementData[] , ... 
[curated-data] [chemistry] [entity]
 

asked by Sterling https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=61736 6 votes

answered by Sterling https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=61736 6 votes

6.22.1.5 DSolve does not return solution to simple system of second order PDEs

https://mathematica.stackexchange.com/landing/r/digest?cta=question&id=230383

I'm trying to solve a simple system of second order PDEs with Mathematica 11.1. 
Here is the system: 
... 
[differential-equations] [equation-solving] [symbolic]
 

asked by C. B. https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=74734 6 votes

answered by bbgodfrey https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=1063 3 votes

6.22.1.6 Build the following symmetric array

https://mathematica.stackexchange.com/landing/r/digest?cta=question&id=230650

My mind is a bit cloudy and I can't quite pinpoint the pattern here that will allow me to write an elegant piece of code to build the following symmetric matrix of for a given size ... 
[matrix] [array] [code-request] [code-golf]
 

asked by QuantumDot https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=2048 5 votes

answered by kglr https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=125 4 votes

6.22.1.7 Evaluate section by button click

https://mathematica.stackexchange.com/landing/r/digest?cta=question&id=230613

I have a section in my notebook devoted to unit testing, since I'm not comfortable to use the built-in system. I'd like to evaluate the entire section by button click. But I get lost in the notebook ... 
[front-end] [notebooks]
 

asked by infinitezero https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=31036 5 votes

answered by Kuba https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=5478 5 votes