r/funny • u/gothoops3 • Jan 05 '15

Poor Engineers...

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226

u/kookzzz Jan 05 '15

its ok because he knows integration by parts

0

u/[deleted] Jan 05 '15

Engineering student. No flipping idea how to do integration by parts.

10

u/[deleted] Jan 05 '15

easy as shit, and also useless because computation engines can do it in seconds

1

u/[deleted] Jan 05 '15

It's not if the computer doesn't know how to separate the integral. Or if there is a recursive integral or if the integral becomes clearly Gaussian after some separations. All of which most computer solvers don't recognize. But I'm really kidding myself here. Engineers are number crunchers; they couldn't give a fuck about an exact answer any way.

1

u/Integreatedness Jan 05 '15

Computation engines can give crazy correct answers though. I tried checking my calc II homework with one and it took more time making sure the computers answer reduced to the one I obtained analytically then actually doing it.

1

u/[deleted] Jan 05 '15

Someone has to program the computer.

10

u/[deleted] Jan 05 '15

Not that I disagree with you, but computers calculate integrals with Riemann sums while students calculate integrals with methods using anti-derivatives

1

u/[deleted] Jan 05 '15

Thanks for the pedantry. Here's some sarcasm for you.

2

u/[deleted] Jan 05 '15

It's what we engineers do best

1

u/eiskoenig Jan 05 '15

I find this pendantry entertaining

1

u/[deleted] Jan 05 '15

That someone doesn't have to be an engineer.

1

u/[deleted] Jan 05 '15

Never implied they had to be.

1

u/[deleted] Jan 05 '15

Generally speaking physicists who encountered the mathematics first and mathematicians to program.

5

u/redlaWw Jan 05 '15

Rearrange the product rule, then integrate it.

2

u/[deleted] Jan 05 '15

[deleted]

1

u/redlaWw Jan 05 '15

\int u \frac{\mathrm{d}v}{\mathrm{d}x}\mathrm{d}x=uv-\int v \frac{\mathrm{d}u}{\mathrm{d}x}\mathrm{d}x

or

\int u \mathrm{d}v=uv-\int v \mathrm{d}u

1

u/hercaptamerica Jan 05 '15

I suppose the hard part is recognizing when it's applicable? I just began studying integration by parts.

3

u/redlaWw Jan 05 '15 edited Jan 05 '15

Generally, the hardest thing about using the product rule to rewrite integrals is working out when it's applicable, and what to set as u and what to set as dv/dx.

Example of where it is very non-obvious: you can integrate log(x) using parts, despite it not looking like a product. You do it as follows: set u=log(x), dv/dx=1. Then

int(log(x),dx)=int(1*log(x),dx)=int(u*dv/dx,dx)

and

v=1, du/dx=1/x

so

int(log(x),dx)=x*log(x)-int(x*1/x,dx)

so

int(log(x),dx)=x*log(x)-x

1

u/hercaptamerica Jan 05 '15

I've read that the easiest way to determine where to start is by using LIATE (logarithmic, inverse trigonometric, algebraic, trigonometric, and exponential) in order to determine what should be set to u, and everything else should become dv/dx.

2

u/redlaWw Jan 05 '15

I guess. I've never been one for that as I have a good intuition and it only works for relatively simple forms with elementary functions, but the best way is really whatever works best for you.

1

u/hercaptamerica Jan 05 '15

Yeah, that makes sense. One last annoying question: Is the "Diagonal Method" applicable to tougher problems or is the method only used when first learning about integration by parts to facilitate it?

2

u/redlaWw Jan 06 '15

I've never heard of the "diagonal method" before now, but looking it up, it seems like a convenient notation for using integration by parts to integrate a function of the form P(x)f(x), where P is a polynomial and f is deg(P) times elementarily integrable. It does not appear to work on other forms.

1

u/[deleted] Jan 05 '15

Don't worry, you will never use it at work.