dharr

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Name: Dr. David Harrington

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Member for: 20 years, 338 days

Company/Institution: University of Victoria

Title: Professor or university staff

Location: Victoria, British Columbia, Canada

Website: http://web.uvic.ca/~dharr

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Contact Dr. David Harrington

I am a retired professor of chemistry at the University of Victoria, BC, Canada. My research areas are electrochemistry and surface science. I have been a user of Maple since about 1990.

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These are answers submitted by dharr

bad RootOf...

Answered: dharr 8205

February 18 2023

2 12

The index=real[4] in the RootOf looks wrong. [Edit: I submitted an SCR].

>	expr := 36a^3b^3+8a^2b^2(9(a+b+1)^2+4(ab+a+b))(a+b+1)+((a-b)^2-2(a+b)+1)^2(a+b+1)^5+ab((a-b)^2-2(a+b)+1)(17(a+b+1)^2+4(ab+a+b))*(a+b+1)^2:

You can use the explicit option so you don't get the RootOf, but then you get only four solutions.

${a = 1, b = 0}, {a = 0, b = 1}, {a = 3^(1/2)-1, b = 1}, {a = 1, b = 1}$

There is something wrong with the RootOf solution, which has index=real[4] instead of index = positive integer
Under the assumption that it was supposed to be an integer, we try various integers and with index=1 one of the RootOfs is resolved, but the other is now not correct (should be 1, but evalf does not give this)

$[{a = 1, b = 0}, {a = RootOf(_Z^7+(2+3^(1/2))*_Z^6+(11*3^(1/2)-18)*_Z^5+(-5*3^(1/2)+4)*_Z^4+(-144*3^(1/2)+251)*_Z^3+(39*3^(1/2)-66)*_Z^2+(981*3^(1/2)-1698)*_Z+873*3^(1/2)-1512, index = 3), b = 3^(1/2)-1}, {a = 0, b = 1}, {a = 3^(1/2)-1, b = 1}, {a = 1, b = 1}, {a = 1/2+(1/2)*3^(1/2), b = 1/2+(1/2)*3^(1/2)}]$

Let's go back and just remove the index from the RootOf

and the correct answer is the first of these values.

Download solve.mw

_EnvUseHeavisideAsUnitStep:=true;...

Answered: dharr 8205

February 16 2023

3 1

Download remove_undefined.mw

numeric values required...

Answered: dharr 8205

February 11 2023

0 0

If I assign some values such as h_n:=[5,4], etc (for np=2) then it works.

points.mw

or a variation more suitable to a large number of points.

points2.mw

some things...

Answered: dharr 8205

February 11 2023

1 0

Your variable s__v_0 actually had an unseen multiplication in. I replaced it with just sv0. Some subscripts were made differently in different places, for example v[1] or v__1; I changed them all to the double-underline form. In your differential equation mu was strange (from a font perhaps instead of typing mu and using escape), and different from the mu in the parameters list. You had two alphas in the parameter list.

You now need to resolve the fact that yor equations have Q(t) but there is no differential equation for Q(t). You have some parameters in your parameter list that are not in your equations - I would have removed them but you give them values later. So next step is to resolve these inconsistencies.

Covid19_Simulation2.mw

alias...

Answered: dharr 8205

February 09 2023

2 0

Alias perhaps comes closest to "doing it automatically".

Download alias.mw

graph...

Answered: dharr 8205

February 09 2023

1 0

I just removed all entries with bonds with H from the table, then made the matrix, rather than deleting rows and columns afterwards; I hope this is equivalent.

graph:=proc(t::table)
  local t2,n,A;
  t2:=remove['flatten'](x->x[1][-1]="H",t);          # remove all entries from table with string ending in "H"
  n:=max(ListTools:-Flatten([indices(t2)]));                   # find Matrix size
  A:=Matrix(n,n,t2,'shape'='symmetric');                       # table to Matrix
  LinearAlgebra:-Map(x->if x::list then x[2] else x end if,A); # keep only weights
  GraphTheory:-Graph(A);
end proc:

Download Graph.mw

Iterator:-SetPartitionFixedSize...

Answered: dharr 8205

February 07 2023

2 0

I was working on this but see @Carl Love was first. Here's a slight variation.

restart;

>	s:={"a","b","c","d","e","f"}:

>	parts:=Iterator:-SetPartitionFixedSize([3,3]);

(1)

First 3 integers are the locations of the first 3, next 3 of the second 3

>	Print(parts,'showrank');

1: 1 2 3 4 5 6
2: 1 2 4 3 5 6
3: 1 2 5 3 4 6
4: 1 2 6 3 4 5
5: 1 3 4 2 5 6
6: 1 3 5 2 4 6
7: 1 3 6 2 4 5
8: 1 4 5 2 3 6
9: 1 4 6 2 3 5
10: 1 5 6 2 3 4

>	for part in parts do {{seq(s[i],i in part[1..3])},{seq(s[i],i in part[4..6])}}; end do;

(2)

Download partitions.mw

2D math...

Answered: dharr 8205

February 03 2023

2 6

Some of the lambda's in vvalue were not formed with the double underline (use lprint vvalue to see this). After fixing this, simplify(...,size) executes in a reasonable time.

Download sol1det.mw

unassigned variables...

Answered: dharr 8205

February 03 2023

0 0

Hard to tell without an uploaded worksheet (use green up-arrow), but it looks like NN and MM weren't given values.

eval...

Answered: dharr 8205

February 01 2023

0 0

To evaluate y at a particular x value use eval (for evaluate). For example,

y:=0.1*x+0.3*x^2;
eval(y,x=2);

gives 1.4

To do a lot of them, set up y as a function (technically a procedure), and put the x values you want in a list:

y:=x->0.1*x+0.3*x^2;
xvals:=[seq(i,i=0..2,0.5)];
y~(xvals)

gives [0., 0.125, 0.400, 0.825, 1.400]

exportplot...

Answered: dharr 8205

January 30 2023

2 5

plottools:-exportplot can export .svg (should also do .tiff but I got an error message). The .svg file looks correct in CorelDraw.

restart;

with(plots):with(plottools):

A := [[[6, 13], [6, 7], [5, 7], [5, 5], [7, 5], [7, 4], [4, 4], [4, 13]], [[13, 13], [13, 20], [20, 20], [20, 23], [22, 23], [22, 22], [23, 22], [23, 16], [16, 16], [16, 9], [9, 9], [9, 6], [7, 6], [7, 7], [6, 7], [6, 13]], [[13, 23], [20, 23], [20, 20], [13, 20]], [[13, 24], [20, 24], [20, 23], [13, 23]], [[22, 24], [22, 23], [20, 23], [20, 24]], [[24, 24], [24, 22], [23, 22], [23, 23], [22, 23], [22, 24]], [[22, 22], [22, 23], [23, 23], [23, 22]], [[22, 25], [25, 25], [25, 16], [23, 16], [23, 22], [24, 22], [24, 24], [22, 24]], [[25, 6], [16, 6], [16, 9], [23, 9], [23, 16], [25, 16]], [[9, 6], [9, 9], [16, 9], [16, 6]], [[6, 6], [6, 7], [7, 7], [7, 6]], [[6, 20], [13, 20], [13, 13], [6, 13]], [[20, 28], [28, 28], [28, 16], [25, 16], [25, 25], [22, 25], [22, 24], [20, 24]], [[16, 5], [9, 5], [9, 6], [16, 6]], [[7, 5], [7, 6], [9, 6], [9, 5]], [[5, 5], [5, 7], [6, 7], [6, 6], [7, 6], [7, 5]], [[4, 23], [13, 23], [13, 20], [6, 20], [6, 13], [4, 13]], [[23, 9], [16, 9], [16, 16], [23, 16]], [[9, 1], [1, 1], [1, 13], [4, 13], [4, 4], [7, 4], [7, 5], [9, 5]]]:
arte := seq(polygonplot([A[i]], color = ColorTools:-Color([rand()/10^12, rand()/10^12, rand()/10^12]), axes = none, style = polygon, view = [1 .. max(A[]), 1 .. max(A[][])]), i = 1 .. nops(A)):
plt:=display(arte):

>	currentdir();

$"C:\Users\dharr\Desktop"$

>	exportplot(cat(currentdir(),"/myplot.svg"),plt);

Download exportplot.mw

K must be real...

Answered: dharr 8205

January 29 2023

0 13

From the ?dsolve,numeric help page "All IVP methods can be used for complex-valued IVPs with a real-valued independent variable". Not sure what it would mean for a complex independent variable - some sort of path through the complex plane would be needed.