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Anonymous Mon 22 Mar 17:29:22 2021 No.12868336 View Reply Original Report

Quoted By: >>12868491 >>12868510 >>12868512

I fucking hate Mathematica

I'm trying to use NDSolve to solve a diffeq, and I want to vary some parameter "a" for a couple different values and output their respective plots. But it fucking WILL NOT cooperate. I hate that I have to use Mathematica for this project this shits so basic i should just be able to iterate over a list but it doesn't work for loops are completely broken. How do I do this

Anonymous

Anonymous Mon 22 Mar 2021 18:17:16 No.12868491 Report

Quoted By: >>12868501

>>12868336
Make sure to use comments in your code so you can come back to it later witha clear head. You sound very frustrated and charged right now. Try going for a jog and clear your head.

Not trying to patronize you at all. This works like a goddamn magic trick

Anonymous

Anonymous Mon 22 Mar 2021 18:20:39 No.12868501 Report

Quoted By:

>>12868491
no i mean i get what youre saying. this is me coming back to it tho, i just dont get how to make this work. i have literally no clue how to do this beyond copy pasting the code. literally any other method would make this trivially easy, like in python or something i could do this in one line. but i was never taught how to do this and despite countless hours of googling i cannot find a way to do this in mathematica. for loops are notoriously shit in it and it sucks

Anonymous

Anonymous Mon 22 Mar 2021 18:21:16 No.12868506 Report

Quoted By: >>12868509

Like asking for advice on /sci/ and following it would not screw things up for you even worse.

Anonymous

Anonymous Mon 22 Mar 2021 18:22:22 No.12868509 Report

Quoted By: >>12868537

>>12868506
its a basic syntactical issue. i just dont know the syntax for repeatedly solving something for different values and plotting them, and i cannot find a single example on the entire goddamn internet of how to do this

Anonymous

Anonymous Mon 22 Mar 2021 18:22:22 No.12868510 Report

Quoted By: >>12868527

>>12868336
>professor gives us copies of his Mathematica work to study
>quiz problem is setup the exact same as one of his practice problems
>copy and paste his functions and change the values
>spits out fucking unsimplified trig and gives me the variables I was trying to solve for in the answers.
I have fucking had it with this program too OP.

Anonymous

Anonymous Mon 22 Mar 2021 18:22:50 No.12868512 Report

Quoted By: >>12868527

>>12868336
Imagine having a program solve shit for you, grow up and solve your own diff equations.

Anonymous

Anonymous Mon 22 Mar 2021 18:26:17 No.12868527 Report

Quoted By:

>>12868510
dude its fucking infuriating
mathematica has some incredible uses, dont get me wrong, it makes my quantum hw infinitely easier. but beyond being a calculator, this program is u s e l e s s
>>12868512
>all diffeqs have closed form solutions
ok buddy

Anonymous

Anonymous Mon 22 Mar 2021 18:29:06 No.12868537 Report

Quoted By: >>12868650

>>12868509
Okay, then show me your code. I have a former phd student who works for Wolfram, he may agree to explain what to do.

Anonymous

Anonymous Mon 22 Mar 2021 18:58:00 No.12868650 Report

Quoted By: >>12868658 >>12868661

>>12868537
That would be delightful. Here's the code I'm starting with. I'm trying to vary the plots for a (ie, output a different plot for a=0.01, 0.05, 0.10). This is the functioning code for a fixed value of a:

Clear["Global`*"]
a = 0.01;
eq = D[u[t, x], t] == a*D[u[t, x], x, x];
ic = u[0, x] == -10*(UnitStep[x] - 1);
bound1 = u[t, -1] == (0.1*t + 1)*10;
bound2 = u[t, 1] == 0;
NDSolve[{eq, ic, bound1, bound2}, u[t, x], {t, 0, 10}, {x, -1, 1}];
Plot3D[Evaluate[u[t, x] /. %], {t, 0, 10}, {x, -1, 1},
PlotRange -> All]

This is my first naive attempt at iterating over a:

Clear["Global`*"]
eq = D[u[t, x], t] == a*D[u[t, x], x, x];
ic = u[0, x] == -10*(UnitStep[x] - 1);
bound1 = u[t, -1] == (0.1*t + 1)*10;
bound2 = u[t, 1] == 0;
For[a = 0.01, a <= 0.05, a += 0.02,
NDSolve[{eq, ic, bound1, bound2}, u[t, x], {t, 0, 10}, {x, -1, 1}]];
Plot3D[Evaluate[u[t, x] /. %], {t, 0, 10}, {x, -1, 1},
PlotRange -> All]

This is my second attempt:

Clear["Global`*"]
eq = D[u[t, x], t] == a*D[u[t, x], x, x];
ic = u[0, x] == -10*(UnitStep[x] - 1);
bound1 = u[t, -1] == (0.1*t + 1)*10;
bound2 = u[t, 1] == 0;
NDSolve[{eq, ic, bound1, bound2}, u[t, x], {t, 0, 10}, {x, -1, 1}];
For[a = 0.01, a <= 0.05, a += 0.02,
Plot3D[Evaluate[u[t, x] /. %], {t, 0, 10}, {x, -1, 1},
PlotRange -> All]]

In the first attempt it's (successfully?) iterating over the list but won't plot it for whatever reason. In the second attempt it can't numerically solve with a left undefined, so it never gets to the plotting bit.

Anonymous

Anonymous Mon 22 Mar 2021 19:02:20 No.12868658 Report

Quoted By: >>12868669

>>12868650
Don't forget to end if.

Anonymous

Anonymous Mon 22 Mar 2021 19:02:38 No.12868661 Report

Quoted By:

>>12868650
I also tried using Do instead of For since someone online recommended this.

Clear["Global`*"]
ic = u[0, x] == -10*(UnitStep[x] - 1);
bound1 = u[t, -1] == (0.1*t + 1)*10;
bound2 = u[t, 1] == 0;
Do[sol =
NDSolve[{eq = D[u[t, x], t] == a*0.01*D[u[t, x], x, x], ic, bound1,
bound2}, u[t, x], {t, 0, 10}, {x, -1, 1}], {i, 1, 5}];
Table[sol, {i, 1, 5}]
Plot3D[Evaluate[u[t, x] /. %], {t, 0, 10}, {x, -1, 1},
PlotRange -> All]

Anonymous

Anonymous Mon 22 Mar 2021 19:03:39 No.12868669 Report

Quoted By:

>>12868658
>end if
what if statement?

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