Message in #general · Neon Genesis Phijkchu

Lute Sep 3, 2020 8:18 PM general

since it doesn't matter when you do it in matlab

Lute Sep 3, 2020 8:18 PM general

glad I could entertain you...

Phijkchu_Pikachu Sep 3, 2020 8:20 PM general

https://www.mathworks.com/matlabcentral/answers/433136-how-do-i-solve-this-projectile-motion-problem

How do I solve this projectile motion problem? - MATLAB Answers - ...

How do I solve this projectile motion problem?. Learn more about physics, projectile motion, sub, solve, dif, syms, trajectory, homework MATLAB

www.mathworks.com

Phijkchu_Pikachu Sep 3, 2020 8:20 PM general

2 seconds of google

Phijkchu_Pikachu Sep 3, 2020 8:20 PM general

try this

Lute Sep 3, 2020 8:22 PM general

literally what I've been trying for the past 2 hours

Lute Sep 3, 2020 8:22 PM general

not helpful

legorhin Sep 3, 2020 8:28 PM general

is all you need to do calling solve then filtering for greater than 0?

Phijkchu_Pikachu Sep 3, 2020 8:29 PM general

yes because his answer will either be the right answer or the negative of that

Lute Sep 3, 2020 8:30 PM general

I think so

Phijkchu_Pikachu Sep 3, 2020 8:30 PM general

Considering I just solved it by hand, yes

Dolfin Sep 3, 2020 8:31 PM general

Cheese

Lute Sep 3, 2020 8:35 PM general

I guess I could do newton raphson iteration but that seems like overkill

legorhin Sep 3, 2020 8:35 PM general

solve([hf==h0+v0*t*sind(theta)-g/2*t*t,
       xf==x0+v0*t*cosd(theta)],
      [v0,t])

legorhin Sep 3, 2020 8:36 PM general

then filter the result

Phijkchu_Pikachu Sep 3, 2020 8:36 PM general

>iteration

Phijkchu_Pikachu Sep 3, 2020 8:36 PM general

for what

Dolfin Sep 3, 2020 8:36 PM general

A week later they fact check saying the cdc didn’t say only 6% were pure covid deaths when they clearly did

Phijkchu_Pikachu Sep 3, 2020 8:36 PM general

you are not solving a variable problem you are solving a system of 2 equations with 1 unknown

legorhin Sep 3, 2020 8:36 PM general

two unknowns

Lute Sep 3, 2020 8:36 PM general

you make a guess for 1 pika

Phijkchu_Pikachu Sep 3, 2020 8:36 PM general

the t cancels

Phijkchu_Pikachu Sep 3, 2020 8:36 PM general

my bad

Phijkchu_Pikachu Sep 3, 2020 8:37 PM general

or does not cancel

Phijkchu_Pikachu Sep 3, 2020 8:37 PM general

rather you solve for it

Phijkchu_Pikachu Sep 3, 2020 8:37 PM general

either way you do not need to guess for either of them

Phijkchu_Pikachu Sep 3, 2020 8:37 PM general

and you do not need iteration

legorhin Sep 3, 2020 8:37 PM general

you being given a degrees value for theta concerns me

Phijkchu_Pikachu Sep 3, 2020 8:38 PM general

I mean, you can just run the solve command twice as a non elegant solution, once for T, the total flight time

Phijkchu_Pikachu Sep 3, 2020 8:38 PM general

and once for V0

Phijkchu_Pikachu Sep 3, 2020 8:39 PM general

but you can only do that in this case because sintheta = costheta = 1/root(2)

legorhin Sep 3, 2020 8:39 PM general

my thing should work, you just need to filter the t values because I don't know what the shape of the resultant is going to be

Lute Sep 3, 2020 8:39 PM general

right and that gives me a struct leg

Lute Sep 3, 2020 8:39 PM general

but how to I extract an answer from that struct

legorhin Sep 3, 2020 8:40 PM general

show me what it looks like

Lute Sep 3, 2020 8:40 PM general

legorhin Sep 3, 2020 8:41 PM general

how do you need to give the answer at the end?

Lute Sep 3, 2020 8:41 PM general

I want to to print something like v0=9.6

legorhin Sep 3, 2020 8:41 PM general

so it is just printing it out?

Lute Sep 3, 2020 8:41 PM general

in the command window

Lute Sep 3, 2020 8:41 PM general

yeah

Lute Sep 3, 2020 8:42 PM general

filtering it and printing it out

Lute Sep 3, 2020 8:42 PM general

everything else I get

legorhin Sep 3, 2020 8:43 PM general

can you do this? disp(ans.v0)

Lute Sep 3, 2020 8:43 PM general

that prints this

Lute Sep 3, 2020 8:43 PM general

Phijkchu_Pikachu Sep 3, 2020 8:44 PM general

is there a simplify command

Lute Sep 3, 2020 8:44 PM general

no idea why it doesn't solve it

Lute Sep 3, 2020 8:44 PM general

that's the big issue I have been having

legorhin Sep 3, 2020 8:44 PM general

what is the data type?

Lute Sep 3, 2020 8:44 PM general

default I guess, not 100% sure what you mean by data type

Phijkchu_Pikachu Sep 3, 2020 8:44 PM general

thats right btw

Phijkchu_Pikachu Sep 3, 2020 8:44 PM general

that is 9.6

Lute Sep 3, 2020 8:44 PM general

I know it is pika....

Phijkchu_Pikachu Sep 3, 2020 8:45 PM general

then it did solve it

Lute Sep 3, 2020 8:45 PM general

I have been getting this for the last 2 hours

legorhin Sep 3, 2020 8:45 PM general

what type of field is v0?

Phijkchu_Pikachu Sep 3, 2020 8:46 PM general

Phijkchu_Pikachu Sep 3, 2020 8:46 PM general

where P(1) was his function evaluated at 1

Lute Sep 3, 2020 8:46 PM general

Lute Sep 3, 2020 8:47 PM general

dunno if this helps

Lute Sep 3, 2020 8:47 PM general

also is there a better way to define v0 and t?

Phijkchu_Pikachu Sep 3, 2020 8:47 PM general

you could specify they are real numbers

Phijkchu_Pikachu Sep 3, 2020 8:47 PM general

and probably specify they are positive

Phijkchu_Pikachu Sep 3, 2020 8:47 PM general

idk

legorhin Sep 3, 2020 8:48 PM general

pika you can force only real solutions and max one solution

Phijkchu_Pikachu Sep 3, 2020 8:49 PM general

I assumed so

legorhin Sep 3, 2020 8:53 PM general

v0t = solve([hf==h0+v0*t*sind(theta)-g/2*t*t,
       xf==x0+v0*t*cosd(theta)],
      [v0,t],'PrincipalValue',true,'Real',true);
disp(v0t);
disp(["v0 = ", double(v0t.v(1)\);
disp(["t = ", double(v0t.t(1)\);

legorhin Sep 3, 2020 8:53 PM general

assuming principle is positive

legorhin Sep 3, 2020 8:54 PM general

this would be so much easier if you could just use the free and more useful python

Lute Sep 3, 2020 8:56 PM general

it doesn't like your notation for it, I might just try to do newton raphson honestly

Lute Sep 3, 2020 8:56 PM general

I get an invalid expression error for the disp(["v0 = ", double(v0t.v(1)); line

legorhin Sep 3, 2020 8:57 PM general

you are trying to overcomplicate something just because you won't bother debugging anything

legorhin Sep 3, 2020 8:58 PM general

v0t = solve([hf==h0+v0*t*sind(theta)-g/2*t*t,
       xf==x0+v0*t*cosd(theta)],
      [v0,t],'PrincipalValue',true,'Real',true);
disp(v0t);
disp(["v0 = ", double(v0t.v(1)]);
disp(["t = ", double(v0t.t(1)]);

legorhin Sep 3, 2020 8:58 PM general

you actually have a parser there to point out typos

Lute Sep 3, 2020 9:12 PM general

still doesn't like that line

legorhin Sep 3, 2020 9:13 PM general

yeah there's a missing )

Lute Sep 3, 2020 9:15 PM general

legorhin Sep 3, 2020 9:15 PM general

then fix it

legorhin Sep 3, 2020 9:15 PM general

these are trivial typos

Dolfin Sep 3, 2020 9:58 PM general

anyways

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